Broad spectrum light source calibration systems and related methods

ABSTRACT

Systems and methods are disclosed for light sources that use the photo-sensitivity of one or more colored LEDs to determine at least a portion of the emission spectrum of a white light source or other broad spectrum light emitter. As described herein, a white LED or other broad spectrum light emitter can be used as the light source, if desired, along with one or more additional colored LEDs, and the same colored LEDs can be used to emit light and to adjust a color point produced by the light source. Applications for the disclosed embodiments include but are not limited to general lighting, LCD backlighting, projectors, and direct emission displays such as OLEDs and digital billboards.

RELATED APPLICATIONS

This application claims priority to the following co-pending provisionalapplications: U.S. Provisional Patent Application Ser. No. 61/273,518filed Aug. 5, 2009 by David J. Knapp and entitled “Display and OpticalPointer Systems and Related Methods;” U.S. Provisional PatentApplication Ser. No. 61/273,536 filed Aug. 5, 2009 by David J. Knapp andentitled “Display Calibration Systems and Related Methods;” U.S.Provisional Patent Application Ser. No. 61/277,871 filed Sep. 30, 2009by David J. Knapp and entitled “LED Calibration Systems and RelatedMethods;” U.S. Provisional Patent Application Ser. No. 61/281,046 filedNov. 12, 2009 by David J. Knapp and entitled “LED Calibration Systemsand Related Methods;” U.S. Provisional Patent Application Ser. No.61/336,242 filed Jan. 19, 2010 by David J. Knapp and entitled“Illumination Devices and Related Systems and Methods;” and U.S.Provisional Patent Application Ser. No. 61/339,273 filed Mar. 2, 2010 byDavid J. Knapp, et al., and entitled “Systems and Methods for VisibleLight Communication;” each of which is hereby incorporated by referencein its entirety.

This application is also a continuation-in-part application of thefollowing co-pending application: U.S. patent application Ser. No.12/803,805 filed on Jul. 7, 2010 by David J. Knapp and entitled“Intelligent Illumination Device;” which in turn claims priority to U.S.Provisional Patent Application Ser. No. 61/224,904 filed on Jul. 12,2009 by David J. Knapp and entitled “Intelligent Illumination Device;”each of which is hereby incorporated by reference in its entirety. Thisapplication is also a continuation-in-part application of the followingco-pending patent applications: U.S. patent application Ser. No.12/360,467 filed Jan. 27, 2009 by David J. Knapp and entitled “FaultTolerant Network Utilizing Bi-Directional Point-to-Point CommunicationsLinks Between Nodes;” and U.S. patent application Ser. No. 12/584,143,filed Sep. 1, 2009 by David J. Knapp and entitled “Optical CommunicationDevice, Method and System;” which in turn claims priority to U.S.Provisional Patent Application Ser. No. 61/094,595 filed on Sep. 5, 2008by David J. Knapp and entitled “Optical Communication Device, Method andSystem;” each of which is hereby incorporated by reference in itsentirety.

This application is also related to the following concurrently filedpatent applications: U.S. patent application Ser. No. ______ filedAugust ______, 2010 by David J. Knapp and entitled “Display and OpticalPointer Systems and Related Methods;” U.S. patent application Ser. No.______ filed August ______, 2010 by David J. Knapp and entitled “DisplayCalibration Systems and Related Methods;” U.S. patent application Ser.No. ______ filed August ______, 2010 by David J. Knapp and entitled “LEDCalibration Systems and Related Methods;” U.S. patent application Ser.No. ______ filed August ______, 2010 by David J. Knapp and entitled“Illumination Devices and Related Systems and Methods;” and U.S. patentapplication Ser. No. ______ filed August ______, 2010 by David J. Knapp,et al., and entitled “Systems and Methods for Visible LightCommunication;” each of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD OF THE INVENTION

The inventions relate to light emitting diodes (LEDs) and systems andmethods that utilize LEDs.

BACKGROUND

Lamps and displays using LEDs for illumination are becoming increasinglypopular in many different markets. LEDs provide a number of advantagesover traditional light sources, such as fluorescent lamps, including lowpower consumption, long lifetime, and no hazardous material, andadditional specific advantages for different applications. For instance,LEDs are rapidly replacing Cold Cathode Fluorescent Lamps (CCFL) as LCDbacklights due to smaller form factor and wider color gamut. LEDs forgeneral illumination provide the opportunity to adjust the color orwhite color temperature for different effects. LED billboards arereplacing paper billboards to enable multiple advertisements totimeshare a single billboard. Further, projectors that use LEDs as thelight source may become popular in mobile handsets, such as smartphones,in the near future. Likewise, Organic LEDs or OLEDs, which usemulti-colored LEDs directly to produce light for each display pixel, andwhich use arrays of organic LEDs constructed on planar substrates, mayalso become popular for many types of display applications.

LED lamps for general illumination and LED backlights for displayspredominately use white LEDs, which typically comprise of a blue LEDcoated with a phosphor that absorbs most of the blue photons from theblue LED and re-emits lower energy photons over a relatively broad rangeof wavelengths. The resulting blended spectral emissions from the bluephotons that are not absorbed by the phosphor and the phosphor convertedphotons can produce white light with various different colortemperatures. Color temperature is a term used to describe the color oflight as related to light produced by a black body radiator withdifferent temperatures. For instance, so called warm white light with acolor temperature of 2500 degrees Kelvin or 2500K has less optical powerin the blue range, while a cool white light with a color temperature of6000K has more optical power in the blue range. As such, the colortemperatures of white LEDs can be adjusted by the thickness of thephosphor layer that absorbs more or less of the blue photons produced bythe blue LED. Further different types of phosphors that re-emit photonsover different wavelength ranges can also adjust white LED colortemperature.

The well known CIE 1931 XY color space diagram illustrates all colorsthat humans can see in a 2-dimensional color space plot, which isrepresented in FIG. 70. The well known black body radiator curve is acurved line that runs though the 2-dimensional color space. Colors thatare not on the black body curve, such as cyan, magenta, and green,cannot be assigned a color temperature. Since there are infinitely morecolors not on the black body curve than on the black body curve andsince phosphor thickness and emission spectrums cannot be preciselycontrolled, it is very difficult to produce white LEDs with a specificand defined color temperature.

Since the phosphor coating in most white LEDs convert high energy bluephotons into lower energy photons in the green, yellow, and red range,the phosphor absorbs energy which reduces the optical efficiency of theLED and produces heat, both of which are not desirable. As such whiteLEDs with high color temperature and more blue content performsignificantly better than white LEDs with low color temperature andsignificant red content. Consequently, some lighting manufacturersproduce low color temperature lamps for general illumination thatcomprise both phosphor coated blue LEDs and red LEDs to produce whitelight with color temperatures in the 2500K range. Likewise, colorfilters in LCD displays that use white LED backlights typically enhancethe relative red spectral content by various means including attenuatingthe blue and green spectral content. Additionally, backlights comprisingwhite and red LEDs have been mentioned in the literature.

Although combining white and red LEDs to produce warmer colortemperatures or more red spectral content improves performanceparameters including energy efficiency and heat dissipation, controllingthe color point is more difficult since the brightness of the red LEDschange differently with temperature, time, and other operatingconditions than the white LEDs. As an example, U.S. Published PatentApplication 2008-0309255 describes an approach for LED downlights fromCree. This application describes a lighting device comprising white andred LEDs, and an additional light sensor that is sensitive only to aportion of the spectrum produced by the combination of white and redLEDs. Additionally, such patent application further describesdifferential amplifier circuits and temperature sensors to control thecolor of the produced light. Not only do the extra components add cost,but since the light sensor is only sensitive to the shorter (bluer)wavelengths produced by the white LEDs, any variation in light intensityproduced by the red LEDs other than variations produced by temperaturechanges, are not compensated. The most significant uncompensatedvariations are produced by LED aging, which causes the brightness of theLEDs and consequently the color produced by the lighting device tochange significantly over time.

The LED industry, which includes LED suppliers such as Cree, Philips,Osram, Nichia, etc, has responded to the difficulty in producingphosphor coated LEDs with precise color points by introducing theconcept of binning. As such, LED customers that order LEDs with aparticular color temperature and brightness will receive LEDs groupedwithin particular color and brightness bins and labeled as such. Toreflect the magnitude of the issue, which is very similar across all LEDsuppliers, Philips Lumileds' Luxeon Rebel datasheet reflects 19different color bins for their cool white LED product and each color binvaries in the CIE 1931 XY color space by about 0.02 or more within eachcolor bin. The well known McAdam ellipse, which arguably identifies thelimits of human color discrimination, is on the order of ten timessmaller. Additionally, only 5 of the 19 color bins for cool white Rebelcomprise the black body radiation curve. For LED lamp and backlightmakers that want to produce products with consistent color, binning is amajor issue.

Although applications such as digital billboards and handheld projectorstypically use red, green, and blue LEDs and not phosphor coated whiteLEDs, some of such applications could benefit from combining a white LEDwith RGB LEDs to produce brighter pictures. In the case of a digitalbillboard, each pixel could comprise a red, a green, a blue, and a whiteLED. In the case of a projector, the light source could comprise one ormore red, green, blue, and white LEDs. Well known image processingalgorithms enable the white LED to produce pixel or image brightness orgrayscale while the red, green, and blue LEDs provide the pixel or imagecolor components. Considering the complexity described in U.S. PublishedPatent Application 2008-0309255 to maintain color balance for just redand white LEDs, extending the traditional approaches to maintain coloracross red, green, blue, and white LEDs, is prohibitively complex andcostly.

Many Active Matrix OLED (AMOLED) displays currently uses pixels madefrom organic red, green, blue, and white pixels. Since such LEDs aregrown together on a single substrate, the matching between LEDs is muchbetter than with inorganic red, green, blue, and white LEDs that may bemanufactured at completely different locations, at different times, andwith different processes. However, although the LEDs may initially matchwell, organic LED brightness degrades relatively rapidly with use, whichcan result in artifacts forming on displays that predominately producethe same image such as a computer background or toolbar. Such artifactsare visible and undesirable.

Among other reasons also, to eliminate or reduce the need for white LEDbinning, to enable red LEDs to be easily combined with white LEDs toproduce warm white light and efficient display backlights, to enablewhite LEDs to be easily combined with RGB LEDs for billboards andprojectors, and to eliminate artifacts burning into AMOLED displays, aneed exists to easily and cost effectively set and maintain a precisecolor point produced by combinations of white and colored LEDs.

SUMMARY OF THE INVENTION

Systems and methods are disclosed for light sources that use thephoto-sensitivity of one or more colored LEDs to determine at least aportion of the emission spectrum of a white light source or other broadspectrum light emitter. As described herein, the white LED or otherbroad spectrum light emitter can be used as the light source, ifdesired, and the same one or more colored LEDs or different LEDs, ifdesired, can be used to emit light and to adjust a color point producedby the light source. Applications for the disclosed embodiments includebut are not limited to general lighting, LCD backlighting, projectors,and direct emission displays such as OLEDs and digital billboards.Various embodiments are described with respect to the drawings below.Other features and variations can also be implemented, if desired, andrelated systems and methods can be utilized, as well.

One embodiment includes a method and system to set a precise colortemperature produced by a substantially white light source, such as aphosphor coated blue LED, or some other broad spectrum light emitter, incombination with one or more colored or substantially mono-chromaticLEDs during the manufacturing of a device, such as an LED lamp, adisplay backlight, a projector, a digital billboard, or AMOLED (ActiveMatrix OLED) display, and to maintain such color temperature over theoperating life of such a device. The method involves analyzing a portionof the spectrum of the white light source or broad spectrum lightemitter using one or more colored LEDs as wavelength selective lightsensors and then using such colored LEDs (or one or more additionaldifferent LEDs if desired) to emit light whereby adjusting the color oflight produced by the combination of the white light source and thecolored LEDs. These LEDs allow for the color point of the light sourceto be adjusted, as desired, based upon the measurements made withrespect to portions of the spectrum of the broad spectrum light emitter.Embodiments further include a light source comprising a white lightsource and colored LEDs, which could be a pixel in a digital billboardor AMOLED, or the entire light source for a lamp, backlight, orprojector, for instance.

The disclosed embodiments apply to any broad spectrum light emitterand/or substantially white light source and any number of colored LEDs.Of particular interest, however, and as described in more detail below,is the combination of red, green, blue, and white LEDs. In such exampleillustration, the red, green, and blue LEDs analyze the spectrum oflight produced by the white LED by each LED operating as a differentwavelength selective light detector. The blue LED measures the blue partof the spectrum, the green LED measures the green plus blue parts of thespectrum, and the red LED measures substantially the entire spectrumwith emphasis on the red and green portions, of the white LED lightsource. Subsequent to such spectral analysis, the red, green, and blueLEDs emit light with intensities adjusted to produce a desired colorpoint when combined with light produced by the white LED.

To reduce optical measurement errors due in particular to variations inLED responsiveness to incident light, further embodiments create ratiosof signals induced on each LED by the white LED and other LEDs that areused to determine relative brightness of each LED to produce the desiredcolor point. For instance and as described in one example herein, thebrightness of the spectrum of the white LED filtered by the red, green,and blue LEDs is determined relative to the brightness of the blue LED.Additionally, the brightness of the green and red LEDs are determinedrelative to the brightness of the blue LED. All such relative brightnesslevels can then be compared to the desired relative brightness levelsbetween the red, green, and blue LEDs and the three different spectralbands produced by the white LED, and the brightness of the red, green,and blue LEDs, and can be adjusted to produce the desired color pointfrom all four LEDs.

Methods for using measured ratios of light are disclosed herein and alsowith respect to additional embodiments described herein, for example,with respect to the third embodiment. The disclosed embodiments includespectral analysis of a substantially white light to compensate forspectral variations in the emissions of such white light source. Themethods described herein are associated with measuring ratios of emittedlight, further comparing such ratios to desired ratios, and furtheradjusting the brightness produced by the LEDs in response to suchratios.

Specifically related to phosphor coated white LEDs, another aspect ofthe disclosed embodiments compensate for common variations between whiteLEDs during manufacturing and variations that occur over time in aparticular LED. The amount of blue light produced by the blue LED thatdoes not get absorbed by the phosphor relative to the amount of lightemitted by the phosphor varies with phosphor thickness and uniformityduring manufacturing and with phosphor degradation over time. With themethods described herein, the amount of blue light relative to theamount of phosphor converted light produced by the white LED can bedetermined and the amount of light produced by associated red, green,and blue LEDs or just red and green LEDs for instance can be adjusted tocompensate for the difference in such ratio from a desired ratio.

The calibration methods and apparatus described herein address issuesfor devices using groups of different colored LEDs directly or asbacklights for illumination. Such calibration methods reduce the needfor specially binned LEDs for the production of lamps, displays, orbacklights, and maintain the color or color temperature of the lightproduced over the operating life of the device.

In one embodiment, the invention is a light source having an adjustablecolor point that includes a broad spectrum light emitter, an LED with apeak emission wavelength within a spectrum of the broad spectrum lightemitter, and a controller configured to use the LED to measure a portionof the spectrum of the broad spectrum light emitter and to use the LEDto produce illumination to adjust a color point of the light source. Ina further embodiment, the LED is a first LED, and the light sourcefurther includes a second LED, and the controller is configured tocompare a signal induced on the first LED by light from the broadspectrum light emitter to a signal induced on the first LED by lightfrom the second LED. In a further embodiment, the broad spectrum lightemitter is a white LED. the white LED can include a blue LED, and thewhite LED can include a material to convert light from one wavelength toother wavelengths. Still further, the material to convert light from onewavelength to other wavelengths can be in physical contact with the blueLED.

In a further embodiment, the peak emission wavelength of the second LEDis within the spectrum of the white LED. Still further, the peakemission wavelength of the second LED can be shorter than the peakemission wavelength of the first LED. Further, the controller can befurther configured to combine a signal produced by the first LED inresponse to light from the white LED and a signal produced by the firstLED in response to light from the second LED to produce a ratio, andwherein the controller is also configured to compare the ratio to adesired ratio. Still further, the controller can be configured to adjusta relative light intensity produced by the broad spectrum light emitterand by the first LED so that the ratio and the desired ratio aresubstantially equal. Still further, the first LED can be green and thesecond LED can be blue.

In a further embodiment, the light source can include a third LED with apeak emission wavelength longer than the first LED peak emissionwavelength. Still further, the controller can be further configured tocombine a signal produced by the third LED in response to light from thewhite LED and a signal produced by the third LED in response to lightfrom the first LED or second LED to produce a ratio, and wherein thecontroller circuitry can be further configured to compare the secondratio to a desired ratio. Still further, the controller can be furtherconfigured to adjust a relative light intensity produced by the lightsource and the first LED or third LED or both the first LED and thirdLED such that the ratio and the desired ratio are substantially equal.

In another embodiment, the invention is a method for adjusting a colorpoint for a light source that includes emitting a spectrum of light witha broad spectrum light emitter, measuring a portion of the spectrum ofthe broad spectrum light emitter using an LED having a peak emissionwavelength within the spectrum of the broad spectrum light emitter, andusing the LED to produce illumination to adjust a color point of thelight source. Further, the method can include comparing a signal inducedon the first LED by light from the broad spectrum light emitter to asignal induced on the first LED by light from a second LED. Stillfurther, the broad spectrum light emitter is a white LED. The white LEDcan include a blue LED, and the white LED can include a material toconvert light from one wavelength to other wavelengths. Still further,the material to convert light from one wavelength to other wavelengthscan be in physical contact with the blue LED.

In a further embodiment, the method can include using a second LEDhaving a peak emission wavelength within the spectrum of the white LED.Still further, the peak emission wavelength of the second LED can beshorter than the peak emission wavelength of the first LED. In a furtherembodiment, the method can include combining a signal produced by thefirst LED in response to light from the white LED and a signal producedby the first LED in response to light from the second LED to produce aratio, and comparing the ratio to a desired ratio. Still further, themethod can include adjusting a relative light intensity produced by thelight source and by the first LED so that the ratio and the desiredratio are substantially equal. In a further embodiment, the first LEDcan be green and the second LED can be blue.

In another embodiment, the method can include providing a third LED witha peak emission wavelength longer than the first LED peak emissionwavelength. Further, the method can include combining a signal producedby the third LED in response to light from the white LED and a signalproduced by the third LED in response to light from the first LED orsecond LED to produce a ratio, and comparing the second ratio to adesired ratio. Still further, the method can include adjusting arelative light intensity produced by the light source and the first LEDor by the lights source and the third LED or the lights source and thefirst and third LEDs such that the ratio and the desired ratio aresubstantially equal.

In a further embodiment, the invention is a controller for a lightsource having an adjustable color point that includes control circuitryconfigured to be coupled to a broad spectrum light emitter and an LEDwith a peak emission wavelength within a spectrum of the broad spectrumlight emitter where the control circuitry is configured to use the LEDto measure a portion of the spectrum of the broad spectrum lightemitter, and output driver circuitry configured to be coupled to thebroad spectrum light emitter and the LED and to use the adjustment LEDto adjust a color point for light from the broad spectrum light emitterand the adjustment LED. In a further embodiment, the LED is a first LED,and the control circuitry is further configured to be coupled to asecond LED where the control circuitry is further configured to comparea signal induced on the first LED by light from the broad spectrum lightemitter to a signal induced on the first LED by light from the secondLED.

In a further embodiment, the control circuitry can be further configuredto combine a signal produced by the first LED in response to light fromthe broad spectrum light emitter and a signal produced by the first LEDin response to light from the second LED to produce a ratio, and whereinthe control circuitry is also configured to compare the ratio to adesired ratio. Still further, wherein the control circuitry is furtherconfigured to adjust a relative light intensity produced by broadspectrum light emitter and by the first LED so that the ratio and thedesired ratio are substantially equal.

As described herein, other embodiments and variations can also beimplemented, if desired, and related systems and methods can beutilized, as well.

DESCRIPTION OF THE DRAWINGS

Other objects and advantages will become apparent upon reading thefollowing detailed descriptions of the different related embodiments andupon reference to the accompanying drawings. It is noted that a numberof different related embodiments are described with respect to thedrawings.

FIG. 1 (Pointer and Display System) is an exemplary system diagram ofthe display and pointer.

FIG. 2 (System Communication Protocol) is an exemplary systemcommunication protocol.

FIG. 3 (OLED Display Block Diagram) is an exemplary block diagram of anOrganic LED (OLED) display.

FIG. 4 (OLED Pixel Block Diagram) is an exemplary block diagram of anOLED pixel.

FIG. 5 (OLED Sub-pixel and Current Sense Circuit Diagrams) is anexemplary circuit diagram of the OLED sub-pixel and current sensecircuits.

FIG. 6 (OLED Display Timing) is an exemplary OLED display timingdiagram.

FIG. 7 (LED Display Architecture) is an exemplary LED displayarchitecture.

FIG. 8 (Driver IC Block Diagram) is an exemplary LED driver IC blockdiagram.

FIG. 9 (LED Display Timing) is an exemplary LED display timing diagram.

FIG. 10 (LED Driver IC Timing) is an exemplary LED driver IC timingdiagram.

FIG. 11 (LCD Display with LED Backlight Block Diagram) is an exemplaryLCD with LED backlight block diagram.

FIG. 12 (LCD Pixel and Driver Circuit Diagram) is an exemplary LCD pixeland driver circuit diagram.

FIG. 13 (LCD and Backlight Timing) is an exemplary LCD and backlighttiming illustration.

FIG. 14 (Display Calibration System) is an exemplary system diagram ofthe display calibration system.

FIG. 15 (OLED Display Block Diagram) is an exemplary block diagram of anOLED display.

FIG. 16 (OLED Pixel Block Diagram) is an exemplary block diagram of anOLED pixel.

FIG. 17 (OLED Sub-pixel and Current Sense Circuit Diagrams) illustratesexemplary OLED sub-pixel and current sense circuit diagrams.

FIG. 18 (LED Display Architecture) is an exemplary LED displayarchitecture.

FIG. 19 (Driver IC Block Diagram) is an exemplary driver IC blockdiagram.

FIG. 20 (Intensity Correction Matrix Block Diagram) is an exemplaryintensity correction matrix block diagram.

FIG. 21 (Intensity and Wavelength Correction Matrix Block Diagram) is anexemplary intensity and wavelength correction matrix block diagram.

FIG. 22 (IV Sense Block Diagram) is an exemplary current and voltagesense block diagram.

FIG. 23 (LCD Display with LED Backlight Block Diagram) is an exemplaryLCD display with LED backlight block diagram.

FIG. 24 (LCD Pixel and Driver Circuit Diagram) is an exemplary LCD pixeland driver circuit diagram.

FIGS. 25A-D illustrate a first step in an exemplary method fordetermining the optical power emitted from a group of LEDs using thephoto-sensitivity of such LEDs and an additional light source.

FIG. 26C-D illustrate a second step in an exemplary method fordetermining the optical power emitted from a group of LEDs using thephoto-sensitivity of such LEDs and an additional light source.

FIG. 27A-D illustrate a first step in an exemplary method fordetermining the relative optical power emitted from a group of LEDsusing the photo-sensitivity of such LEDs without an additional lightsource.

FIG. 28A-D illustrate a second step an exemplary method for determiningthe relative optical power emitted from a group of LEDs using thephoto-sensitivity of such LEDs without an additional light source.

FIG. 29 is an exemplary block diagram for circuitry to implement themethods illustrated in FIGS. 25A-D, 26A-D, 27A-D and 28A-D.

FIG. 30 is an exemplary block diagram a color correction matrix thatcompensates for LED intensity variations.

FIG. 31A-C illustrate an exemplary method to determine the peak emissionwavelength of light produced by an LED by measuring thephoto-sensitivity of the LED.

FIG. 32 is an exemplary block diagram for a color correction matrix thatcompensates for LED intensity and wavelength variations.

FIG. 33 is a simplified example block diagram for a typical LCD.

FIG. 34 is a simplified example block diagram for a Field SequentialColor (FSC) LCD.

FIG. 35 is a mechanical drawing of an illumination device that uses asilicon photodiode, or other light detecting device, integrated into anLED controller to measure the light produced by red, green, and blueLEDs.

FIG. 36 is a block diagram of an exemplary LED controller withintegrated photodiode.

FIG. 37 is a block diagram of exemplary temperature and photodiodecurrent measurement circuitry using an integrated photodiode.

FIG. 38 is an exemplary connection diagram for multiple illuminationdevices with integrated photodiodes in a display backlight.

FIG. 39 depicts a timing diagram for the power supplies to and the lightoutput from an illumination device with an integrated photodiode.

FIG. 40 is a mechanical drawing of an illumination device that uses adiscreet silicon photodiode, or other light detecting device, to measurethe light produced by red, green, and blue LEDs.

FIG. 41 is a block diagram of an exemplary LED controller that uses adiscreet photodiode to measure the light from LEDs.

FIG. 42 is a block diagram of exemplary temperature and photodiodecurrent measurement circuitry using a discreet photodiode.

FIG. 43 is an exemplary connection diagram for multiple illuminationdevices with discreet photodiodes in a display backlight.

FIG. 44 depicts a timing diagram for the power supplies to and the lightoutput from an illumination device with a discreet photodiode.

FIG. 45 is a block diagram for exemplary color adjustment circuitry.

FIG. 46 is a block diagram for exemplary matrix multiplicationcircuitry.

FIG. 47 is a simplified example block diagram for a typical LCD.

FIG. 48 is a simplified example block diagram for a Field SequentialColor (FSC) LCD.

FIG. 49 an exemplary system diagram of an illumination device and aremote controller.

FIG. 50 is an exemplary list of functions performable by an exemplaryillumination device.

FIG. 51 is an exemplary timing diagram of data communication between theillumination device and the remote controller.

FIG. 52 is an exemplary timing diagram of the bit timing and codingscheme for transferring data between the illumination device and theremote controller.

FIG. 53 is an exemplary illumination device block diagram.

FIG. 54 is an exemplary diagram of a lighting system comprisingillumination devices and remote controller.

FIG. 55 is an exemplary timing diagram for communication within thelight system.

FIG. 56 is a diagram of an exemplary data frame for communicating datawith the lighting system.

FIG. 57 is an exemplary block diagram of an illumination device.

FIG. 58 is an exemplary block diagram for a receiver module within anillumination device.

FIG. 59 is an exemplary block diagram for a PLL and timing module withinan illumination device.

FIG. 60 is an exemplary detailed receive timing diagram.

FIG. 61 is an exemplary block diagram for color calibration circuitry toset and maintain a precise color emitted by red, green, blue, and whiteLEDs.

FIG. 62 is an exemplary block diagram for circuitry to sensephotocurrents from the LEDs.

FIG. 63 illustrates exemplary emission spectra of red, green, blue, andwhite LEDs.

FIG. 64 illustrates exemplary differences in white LED emissionspectrum.

FIG. 65 illustrates exemplary spectral characteristics of red, green,and blue LEDs when operating as light detectors.

FIG. 66A-D illustrate an exemplary first step in an exemplary method toset and maintain a precise color emitted by red, green, blue, and whiteLEDs.

FIG. 67A-D illustrate an alternative exemplary first step in anexemplary method to set and maintain a precise color emitted by red,green, blue, and white LEDs.

FIG. 68A-D illustrate an alternative exemplary second step in anexemplary method to set and maintain a precise color emitted by red,green, blue, and white LEDs.

FIG. 69A-D illustrates an alternative exemplary third step in anexemplary method to set and maintain a precise color emitted by red,green, blue, and white LEDs.

FIG. 70 is a color diagram illustrating an exemplary color adjustmentstep in the exemplary method to set and maintain a precise color emittedby red, green, blue, and white LEDs.

FIG. 71 is an exemplary block diagram for measuring optical poweremitted from an LED.

FIG. 72 is an exemplary circuit diagram for measuring optical poweremitted from an LED with another LED.

FIG. 73A-C illustrates an exemplary method for approximately determiningthe optical power emitted from a group of LEDs using thephoto-sensitivity of such LEDs.

FIG. 74A-D illustrate an exemplary method determining the optical poweremitted from a group of LEDs using a light source as a reference.

FIGS. 75A-F illustrate exemplary methods to improve the accuracy of themethod illustrated in FIG. 3.

FIG. 76A-D illustrate an exemplary method to determine the optical poweremitted from a group of LEDs relative to each other.

FIG. 77 is an exemplary block diagram for circuitry to implement themethods illustrated in FIGS. 73A-C, 74A-D, 75A-F, and 76A-D.

FIG. 78 is an exemplary block diagram a color correction matrix thatcompensated for LED intensity variations.

FIG. 79A-C illustrates an exemplary method to determine the peakemission wavelength of light produced by an LED by measuring thephoto-sensitivity of the LED.

FIG. 80 is an exemplary block diagram for a color correction matrix thatcompensates for LED intensity and wavelength variations.

While the embodiments are susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the inventions to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present embodiments.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various embodiments are described herein that utilize light emittingdiodes (LEDs) for emitting light, for receiving light from lightsources, for detecting light emissions and for various other purposesand applications. While the following eight embodiments describedifferent aspects for the use of LEDs, they are also related. As such,the disclosed embodiments can be combined and utilized with respect toeach other as desired. For example, the calibration and detectionsystems and methods described with respect to the second, third, seventhand eighth embodiments can be utilized with the various illuminationdevices described herein with respect to all embodiments. It is alsonoted that the various disclosed embodiments can be utilized in avariety of applications, including liquid crystal displays (LCDs), LCDbacklights, digital billboards, organic LED displays, AMOLED (ActiveMatrix OLED) displays, LED lamps, lighting systems, lights withinconventional socket connections, projection systems, portable projectorsand/or other display, light or lighting related applications. It is alsonoted that as used herein “r” designations and subscripts typicallyrefer to the color red, “g” designations and subscripts typically referto the color green, “b” designations and subscripts typically refer tothe color blue, and “w” designations and subscripts typically refer tothe color white.

It is further noted that as used herein an illumination device isgenerally intended to include any of a wide variety of devices, systemsor other apparatus or assemblies that produce light using one or morelight sources, including light sources that are implemented using one ormore LEDs. LEDs that can be utilized in the embodiments described hereininclude conventional LEDs, organic LEDs (OLEDs), and any other desiredLED. The illumination devices can be implemented in any desired formand/or application including being used within display devices, LCDs,LCD backlights, digital billboards, organic LED displays, AMOLED (ActiveMatrix OLED) displays, LED lamps, lighting systems, lights withinconventional socket connections, projection systems, portable projectorsand/or any other desired application that utilizes light sources,including LED light sources, and LEDs and/or other light detectors todetect emitted light. As such, it should be understood that theembodiments described below provide example applications andimplementations and should not be considered as limiting. Rather, thetechniques, methods and structures described herein for emitting light,detecting light emissions and adjusting light emissions can be used inany desired device, system or application where light is emitted,detected or adjusted, particularly in combination with the use of LEDsfor emitting light, detecting light emissions and/or adjusting lightemissions. Further, integrated circuits and/or combinations ofintegrated circuits and other circuitry, whether discreet or integrated,can be used to implement the techniques, methods and structuresdescribed herein, as desired. The integrated circuits and/or othercircuitry can be combined with light sources, such as LEDs, to formillumination devices for use with the techniques, methods and structuresdescribed herein for emitting light, detecting light emissions andadjusting light emissions. It is further noted that as described herein,an LED can be implemented as a discreet LED, an integrated LED, a set ofserially connected LEDs, parallel sets of serially connected LEDs orother combinations of LEDs, as desired, depending upon the applicationand implementation desired.

It is further noted that an illumination device as used herein isgenerally intended to include any device or apparatus that emits lightto illuminate an area or another object with visible light, for example,for purposes of being viewed or seen by human eyes, such as would beprovided in or by a lamp, lighting system, display system, OLED panel,LCD panel, projector, billboard and/or any other device or apparatusthat produces visible light for purposes of being viewed by human eyesor by some other viewing system as visible light. In this sense, adevice or apparatus that uses light solely for communication purposeswould likely not be an illumination device as generally used herein.

Example embodiments will now be described with respect to the drawings.The first embodiment describes the use of the techniques, methods andstructures described herein with respect to display devices and opticalpointing systems. The second embodiment describes the use of thetechniques, methods and structures described herein with respect tocalibration of display systems. The third embodiment describes the useof the techniques, methods and structures described herein with respectto LED calibration. The fourth embodiment describes the use of thetechniques, methods and structures described herein with respect tovarious illumination devices. The fifth embodiment describes the use ofthe techniques, methods and structures described herein with respect tointelligent LED lights. The sixth embodiment describes the use of thetechniques, methods and structures described herein with respect tosynchronization of visible light communications. The seventh embodimentdescribes the use of the techniques, methods and structures describedherein with respect to calibration of broad spectrum light emittersincluding white light emitters. And the eighth embodiment provides aalternative description of techniques, methods and structures for LEDcalibration. As noted above, these embodiments can be used alone or incombination with each other, as desired, to take advantage of thetechniques, methods and structures described herein for emitting light,detecting light emissions, and adjusting light emissions, particularlyusing LEDs.

It is further noted that the operational blocks and circuitry shown anddescribed with respect to the block diagrams depicted herein, forexample, in FIGS. 3, 7, 8, 11, 15, 18, 19, 20, 21, 22, 23, 29, 30, 32,36, 37, 38, 41, 42, 43 45, 46, 53, 57, 58, 59, 61, 62, 77, 78 and 80,can be implemented using any desired circuitry including integratedcircuitry, non-integrated circuitry or a combination of integrated andnon-integrated circuitry, as desired. Further, it is noted thatprogrammable or programmed circuitry, such as digital signal processors(DSPs), microprocessors, microcontrollers and/or other programmable orprogrammed circuitry, can also be used with respect to these blocks.Further, software, firmware or other code can be utilized along withthis circuitry to implement the functionality as described herein, ifdesired.

First Embodiment

Display and optical pointer systems and related methods are disclosedthat utilize LEDs in a display device to respond to optical signals fromoptical pointing devices. Various embodiments are described with respectto the drawings below. Other features and variations can also beimplemented, if desired, and related systems and methods can beutilized, as well.

In part, the disclosed embodiments relate to displays with arrays ofLEDs and associated pointing devices that communicate with individualLEDs in the arrays using visible light. The LED arrays can produceimages directly as in LED billboards and sports arena scoreboards or canproduce the backlight for LCD screens for instance. The pointing devicescommunicate with individual pixels or groups of pixels using a beam oflight that may or may not be modulated with data, which is detected bythe LEDs in the array that are exposed to the beam. Periodically, theLEDs in an array stop producing light and are configured with anassociated driver device to detect light from the pointing device. Sucha configuration enables the user to point and click at on screendisplays much like a computer mouse.

One improved system, as described herein, uses an optical pointingdevice, such as a laser pointer or flashlight, to control a graphicaluser interface for instance, on an LCD display with LED backlights or adisplay made from an array of organic or conventional LEDs. As an imageis scanned across such a display, there are times every frame when theLEDs are not producing light. During such light off times, the LEDs areused to detect the presence or absence of light from the opticalpointing device. The graphics controller processes such information overa series of frames to detect a pattern of light from the pointing deviceilluminating a particular location on the display and takes theappropriate action. Such action could be among other things selecting anitem in a menu, dragging and dropping an item, or popping up a menu.

The simplest pointing device could be a laser pointer or flashlight witha single on/off button. With a display playing a video or a televisionbroadcast for instance, the display could pop up a main menu over partof the screen in response to a bright spot of light detected anywhere onthe display. Once the spot is positioned over a particular item in themenu, such as change channel for a television, and then turned off andon again, the appropriate action could be taken. With a display, such asa billboard, advertising merchandise for instance, patterns of light onand off from a pointing device could cause the display to provide moreinformation about a particular item. These are just some examples ofinteractions between a display and a pointing device, with many morepossible.

With more sophisticated pointing devices and displays, data could becommunicated from the pointing device to the display and potentiallyeven from the display to pointing device. For instance, a laser pointerspecially modified to produce light modulated with data could transmitpersonal information, such as an email address, to a display, such as abillboard. A user could instruct the display to send more information toan email address in this example. Again, this example is just one ofmany possible data communication applications.

The types of displays addressed herein include any that use LEDs forillumination, but typically can be divided into three categories,Organic LED (OLED) displays, conventional LED displays, and liquidcrystal displays (LCDs) with LED backlighting. OLED displays typicallycomprise a piece of glass with thin film transistors and LEDs made fromorganic compounds grown on one side to produce an array of pixelstypically comprising red, green, blue, and white sub-pixels. Eachsub-pixel typically has a current source made from the thin filmtransistors that is controlled by column and row drivers typicallysituated on two sides of the perimeter of the glass. The row driverstypically produce a logic level write signal to a row of pixels orsub-pixels while the column drivers produce an analog voltagecorresponding to the desired sub-pixel current. Such voltage istypically stored on a capacitor in each pixel or sub-pixel.

Video images are typically displayed one row at a time as the rowdrivers sequence the write signals to the OLED array typically from thetop to bottom of the array. Moving images are produced a series of stillimages or frames displayed over time. As one image is displayed one rowat a time, the previous image is removed one row at a time. To preventthe well known visual effect called “motion blur”. Every row of LEDs isturned off for a period of time, which removes the previous frame,before displaying a line of the current frame. A high speed snapshot ofan OLED display properly designed to reduce motion blur will show a bandof LED rows illuminated with the rest of the display is dark. The rowdrivers typically write to each row of pixels or sub-pixels twice perframe in order to turn the LEDs on and then off.

The spot on the display illuminated by the pointing device is detectedone row at a time. According to one embodiment, the row drivers producesense signals sequentially to each pixel or sub-pixel row at some offsetfrom the rows producing light to prevent optical crosstalk from the rowsproducing light to the row detecting light. When a sense signal isactive, each sub-pixel in the row can produce a current if the voltageinduced across the associated LED by incident light is greater than acertain level, which can then be detected across the columns by currentsense circuitry associated with the column drivers. The graphicscontroller monitors the current sense circuitry output for each row overa frame to determine the location of the illumination from the pointingdevice, and over many frames to determine the action to take.

Although OLED pixels typically comprise a number of different coloredLEDs, such as red, green, blue, and white, typically only one color isused to detect the illumination from the pointing device. For instance,if a red laser pointer is used as the pointing device, the redsub-pixels in the display are used to detect the illumination. If aflashlight producing white light is the pointing device, the red orgreen sub-pixels in the display may be used to detect the illuminationdepending on the spectrum of the white light.

Displays made from conventional LEDs, which typically comprise of theelement Gallium and are individually packaged, typically are very largeand are used for billboards or video displays in sports stadiums. Aswith small OLED displays, each pixel typically comprises red, green, andblue sub-pixels, but typically do not have white sub-pixels. Eachsub-pixel LED typically is driven by a current source from an LED driverIC (integrated circuit), which typically comprises a number of currentsources associated with a number of sub-pixels. Such ICs can be seriallyconnected together and through a network interface IC to a graphicscontroller, which produces the pixel data, receives the location of theillumination from the pointing device, and takes the appropriate action.

Each driver IC comprises a current source controlled by a pulse widthmodulator to produce light from each associated LED, and a comparator todetect light incident on each LED. Unlike the OLED display, each LED isdriven with a fixed current for a variable amount time, instead of avariable current for fixed amount of time. The pulse width modulatorassociated with each LED receives a digital value from the graphicscontroller each frame and turns on the associated current source for aproportional amount of time. The maximum digital value corresponds to amaximum amount of time the current source can be on, which should beless than a frame period to prevent motion blur.

During the time between frames when the current source associated with aparticular LED is guaranteed to be off, the illumination from thepointing device can be detected. If the voltage induced across the LEDby incident light is greater than a certain value, the associatedcomparator output goes high indicating the presence of light from thepointing device. If the induced voltage is less than the certain amount,the comparator output is low indicating the absence of light. The stateof all the comparator outputs is communicated back to the graphicscontroller for processing.

Like the OLED display, a conventional LED display is typically scannedone row or column at a time, which at any one time produces a band ofilluminated LEDs across the display. The rest of the display is dark. Toprevent optical crosstalk from LEDs producing light to LEDs detectinglight, each LED driver IC typically samples the comparator outputs whenthe associated LEDs are located near the middle of the dark region.

Liquid crystal displays modulate the amount of light produced by abacklight to create an image on the screen. Backlights comprising LEDstypically come in one of two versions. For smaller displays on a laptopcomputer for instance, LEDs situated along one side of the displayinject light into a diffuser that produces uniform white light acrossthe display. For large screen televisions using LED backlights, the LEDsare typically arranged in an array, like the conventional LED display,behind the liquid crystal pixel array. The amount of light produced byeach LED or group of LEDs can be adjusted per frame to increase thecontrast ratio in a manner called “local dimming”, which not possiblefor LCDs with fluorescent backlights or LED backlights situated alongone side of the display.

LED backlights for LCDs typically comprise of either white LEDs, whichare made from blue LEDs with a yellow phosphor coating, or a combinationof red, green, and blue LEDs, for instance. One embodiment uses coloredLEDs configured in an array, like a conventional LED display, for LCDbacklighting.

A liquid crystal pixel array typically comprises a thin film transistorand capacitor associated with each liquid crystal sub-pixel. Thetransparency of the liquid crystal sub-pixel is determined by thevoltage held on the capacitor and is controlled by the associated rowand column drivers. Like the OLED display, the liquid crystal array istypically written one row at a time when the associated logic levelwrite signal goes active. The analog voltages from the column driversare then transferred on to the capacitors through the transistors ineach pixel element in the row. Typically, this analog voltage is heldfor one frame period, until that row is programmed with data for thenext frame.

To reduce motion blur, the backlight array can be scanned so that thedisplay only produces light from any given row for a portion of a frameperiod. A band of light produced by the LED backlight array follows theupdating of the liquid crystal rows by a fixed offset to allow theliquid crystal element time to settle. The LEDs in the backlight arraycan be connected to the same driver ICs described for conventional LEDdisplays, which produce a fixed current for a variable amount of time toproduce light from the LEDs and monitor the voltage induced across theLEDs by incident light to detect the illumination from the pointingdevice.

Just like the conventional LED display, the LED backlight array coulddetect light from the pointing device when each row of LEDs is notproducing light. However, if the image being displayed is very dark,then the liquid crystal elements will block light both from and to thebacklight. During such scenes, the LED array may not be able to detectthe light from the pointing device. To improve this sensitivity, eachliquid crystal row could be set to fully transparent for some period oftime prior to being programmed with data for the next image, which wouldcreate a band of transparent liquid crystal following the band of lightfrom the backlight with some fixed offset. Behind this transparent band,the LEDs, which are not producing light, could detect light from thepointing device. Such a system typically requires the liquid crystalarray to be written twice as often or requires additional circuitry andsignals in each pixel element, and could degrade the contrast ratio dueto light leakage from the backlight through the transparent band.

One embodiment maintains high contrast ratio and lower liquid crystalupdate rates, prevents motion blur, and detects signals from thepointing device by inserting a short dark frame between image frames. Atthe end of each frame, the entire backlight is first turned off, andthen the entire liquid crystal array is set to be fully transparent byenabling all row write signals simultaneously and holding all columndata signals to the voltage associated with transparency. While theliquid crystal is transparent, the driver ICs monitor the voltageinduced across the connected LEDs to detect illumination from thepointing device, and report the results to the graphics controller.Finally, the entire liquid crystal array is set to be opaque, byenabling all row write signals simultaneously and holding all columndata signals to the voltage associated with opaque, just prior toscanning the next frame.

The improved display and pointer systems described herein address issueswith displays using LEDs directly or as backlights for illumination.Bulky and confusing television remote controllers can be replaced by asimple laser pointer or flashlight, and advertiser's effectiveness canbe improved by providing audiences an interactive experience.

As stated above, this first embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to the second, third, seventhand eighth embodiments can be used with respect to the display systemsand methods described in this first embodiment, as desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to display systems and methods described in this firstembodiment, as desired. Further, as stated above, the structures,techniques, systems and methods described with respect to this firstembodiment can be used in the other embodiments described herein, andcan be used in any desired lighting related application, includingliquid crystal displays (LCDs), LCD backlights, digital billboards,organic LED displays, AMOLED (Active Matrix OLED) displays, LED lamps,lighting systems, lights within conventional socket connections,projection systems, portable projectors and/or other display, light orlighting related applications.

Turning now to the drawings, FIG. 1 is one example of pointer anddisplay system 10 that comprises the display 11 and pointer 12. Display11 comprises light emitting diodes (LEDs) for image illumination eitherdirectly in the case of OLED or conventional LED displays, orbacklighting in the case of Liquid Crystal Displays (LCDs). LEDs ofpreferentially different colors, for instance red, green, and blue,produce the wide gamut of colors typically necessary for accuraterepresentation of images either directly in the case of OLED or LEDdisplays, or modulated by an LCD.

Pointer 12 preferentially comprises a button 15 that when depresedcauses pointer 12 to produce beam 16 and when released removes beam 16.Beam 16 is preferentially produced by a red laser pointer, but could beany color or combinations of colors including white. Also beam 16 couldbe produced by an LED or multiple LEDs, an incandescent flashlight, orany other possible source of light. When pointer 12 is aimed at display11 and button 15 is depressed, beam 16 produces spot 14 on display 11.Display 11 detects spot 14 and preferentially produces interactive menu13. By moving spot 14 around display 11 and depressing and releasingbutton 15 at appropriate times, system 10 can operate much a computerand a computer mouse.

Spot 14 is detected by display 11 preferentially during visuallyimperceptible times when the LEDs comprising the pixels or backlightsare turned off. Beam 16 induces a voltage on those LEDs that areilluminated under spot 14 with the appropriate wavelength, which isdetected and processed by the display. Sequences of button 15 clicks incombination with the location of spot 14 enable a user to pop up menus,navigate through a graphical user interface, and drag and drop itemsamong many other things.

FIG. 1 is one example of many possible display and pointer systems 10.For example, pointer 12 can have multiple buttons or no buttons. Beam 16could be computer generated and controlled for instance, and could bemodulated with data to communicate more information to display 11.Display 11 could modulate light from individual pixels to communicateback to pointer 15, to another display 11, or some other electronicdevice.

FIG. 2 is an example of a simple communication protocol for system 10,which shows the button state 26 of button 15, the optical output state27 of beam 16, and the states 28 of display 11 as a function of time.The high state of button 15 represents the button released, while thelow state represents the button depressed. The high state of beam 16represents light being produced by pointer 12, while the low staterepresents no light. Display 11 states S0 through S6 represent one ofmany possible temporal and spatial combinations of spot 14 to select anitem from main menu 20.

Display 11 state S0 represents normal operation of the display, forinstance, when displaying a video or a television broadcast. State S1 isentered time Ton1 after button 15 is depressed, which produces beam 16and spot 14. In state 51, main menu 20 is overlaid on the video forinstance, which is being played. State S2 illustrates when spot 14 ispositioned by the user over the appropriate main menu 20 item to beselected. Display 11 enters state S3 when button 15 is released and beam16 turns off. Provided button 15 is depressed and beam 16 is producedwithin time Tsel, display 11 enters state S4. Display 11 detects theshort off time of beam 16 and responds time Ton2 later with sub-menu 21for instance in state S5. In this example, items from sub-menu 21 arenot needed and state S6 is entered when button 15 is released and beam16 turns off. Time Toff later, display 11 returns to the normaloperating state S0.

The example protocol illustrated in FIG. 2 is one of many possibledifferent means to communicate or control display 11. For instance,button 15 could be double clicked to drag and drop items or differentbuttons could produce different codes or colors of light to indicatedifferent things. As another possibility, pointer 12, another display11, or another electronic devices could synchronize to the periodiclight off periods and communicate high bandwidth data across display 11.

FIG. 3 is an example block diagram of OLED display 11 comprising LEDarray 33 with R rows and C columns of sub-pixel LEDs typically arrangedin pixels of one red, one green, one blue, and one white sub-pixel LED.LED array 33 comprises R/2 rows and C/2 columns of such sub-pixels. Eachsub-pixel LED is configured to produce a certain amount of light by acombination of voltages on a particular WR (write) signal produced byrow driver 32 and DATA signal produced by column driver 31. When a WRsignal is high, the analog voltage on each DATA signal is programmedinto the row of LEDs activated by the particular WR signal.

Power supply 35 produces the main power Vdd for LED array 33 and thereference voltages Vr and Vc for detecting spot 14 preferentially on redsub-pixels. When one of the SNS (sense) signals from row driver 32 goeshigh, the IOUT signals from the LED array 33 source current into currentsense 34 for red sub-pixels in the row activated by a particular SNSsignal when illuminated by spot 14. No current is present on the IOUTsignals associated with red sub-pixels not illuminated by spot 14.Current sense 34 produces an SOUT logic level signal in response to eachIOUT input, which are detected and processed by graphics and timingcontrol circuitry 30. Graphics and timing control circuitry 30, whichalso produces the timing for row driver 32 and the data for columndriver 31, combines the SOUT inputs with timing to determine preciselywhich sub-pixels are illuminated by spot 14.

FIG. 3 is just one of many possible block diagrams for display 11, whichcould be built using any one of a wide range of technologies includingbut not limited to discreet inorganic LED arrays or liquid crystals.Likewise, the block diagram for display 11 built with OLEDs could besubstantially different. For instance, if LED array 33 comprised morecomplex pixel and sub-pixel circuitry, such sub-pixels could becalibrated by additional external circuitry to eliminate variations inLED light output and drive current, or multiplexed by a set of enablesignals to reduce the sub-pixel circuitry. The block diagrams of such anLED display 11 would be substantially different.

FIG. 4 is an example block diagram of OLED pixel 40 in LED array 33referenced by row coordinates I and I+1, and column coordinates J andJ+1, and comprising red sub-pixel 41, green sub-pixel 42, blue sub-pixel43, white sub-pixel 44, and comparator 45. The circuitry in allsub-pixels is the same except the color of the included LED. Redsub-pixel 41 is different only in that the Vled signal is connected tocomparator 45, which compares the voltage on the anode of the red LED toVr and sources current to IOUT(j/2) when red sub-pixel 41 is illuminatedby spot 14 and SNS(i/2) is active. Signals WR(i) and DATA(j) program thelight produced by red sub-pixel 41, signals WR(i) and DATA(j+1) programthe light produced by white sub-pixel 44, signals WR(i+1) and DATA(j)program the light produced by green sub-pixel 42, and signals WR(i+1)and DATA(j+1) program the light produced by blue sub-pixel 43. Allsub-pixels are powered by VDD.

FIG. 4 is just one of many possible pixel 40 block diagrams. Forinstance, any combinations of colors or just one color could be used.Additionally, LEDs of any or all colors could be used to detect one ormore instances of spot 14, or one or more data communication lightchannels. All sub-pixels could be accessed by one WR signal and one DATAsignal if two enable signals select between the sub-pixels.

FIG. 5 is an example circuit diagram for red sub-pixel 41, comparator45, and an individual current sense element in current sense 34referenced by coordinate J. When producing light, LED 56 is driven bythe current through transistor 50, which is set by the voltage stored oncapacitor 55 and the gate of transistor 50. The voltage on capacitor 55is set to the voltage on DATA(j) signal when WR(i) signal is high. WhenWR(i) goes low, capacitor 55 holds the voltage so that DATA(j) can beused to program the current in other rows of sub-pixels when other WRsignals go high. All the sub-pixels connected to WR(i) are programmedsimultaneously by all the DATA signals when WR(i) is high.

To detect light from spot 14, transistor 50 is first turned off byprogramming the voltage across capacitor 50 to zero volts or some valueless than transistor 50 threshold voltage. Then SNS(i/2) signal goes lowto produce a current through transistor 52, which is steered to groundthrough transistor 54 when the voltage across LED 56 is less thanreference voltage Vr and to IOUT(j/2) through transistor 53 when thevoltage across LED 56 is greater than Vr. SNS(i/2) is connected totransistor 52 in all red sub-pixels 41 in the I/2 row of LED array 33.VDD is connected to all sub-pixels and Vr is connected to comparator 45s in LED array 33. All components in pixel 40 are typically processedusing thin film technology.

Current sourced by red sub-pixel 41 into current sense 34 element J isconverted to a voltage by resistor 57 and amplifier 58, and such voltageis compared to reference voltage Vc through comparator 59. The voltageinduced on LED 56 by spot 14 can vary from a few millivolts to a couplevolts. Reference voltage Vr is set to a value high enough to preventambient light from causing comparator 45 to source current on IOUT, butlow enough for display 11 to detect a spot 14 with low optical power.Voltage settings for Vr could be adjusted dynamically based on theambient light level incident on display 11, but typically would residein the range of 500 mV to 1V. Since the signal Vr is connected to thePositive input terminal of amplifier 58, the voltage of the IOUT is heldvery close to Vr through feedback resistor 57. The output of amplifier58 drops below reference voltage Vr when current is sourced bycomparator 45. Reference voltage Vc is connected to the positiveterminal of comparator 59. When the output of amplifier 58 drops belowVc, current sense 34 output SOUT(j) goes high. The reference voltage Vcshould be set to be less than the reference voltage Vr by an amountsufficient to reject noise. Vc is typically about half Vr.

FIG. 5 is one of many possible circuit diagrams for sub-pixels and spot14 detection. For instance, the sub-pixel circuitry could include thecapability to calibrate out variations in transistor 50 thresholdvoltage or in LED 56 output light. Comparator 45 could includeadditional transistors to output a voltage instead of a current, orphoto generated current instead of voltage from LED 56 could bedetected. An additionally signal could be used to turn off the currentinto LED 56 instead of using the WR(i) signal. Many other circuitconfigurations are possible.

FIG. 6 is an example illustration of display 11 timing for a HighDefinition (HD) TV with 1080 rows of pixels that shows how images arescanned and spot 14 is detected. FIG. 6 includes four snapshots 60 ofdisplay 11 at times T0, T1, T2, and T3 within one frame period. A frameis a single image in a sequence that produces a video or motion pictureand a frame period is the time from the start of presentation of a firstframe to the start of presentation of a second frame. Below thesnapshots 60 are detailed timing diagrams 61 for the input and outputsignals for a red sub-pixel 41 that is illuminated with coordinates(1080,j) and not illuminated with coordinates (1082,j).

At time T0, frame N begins to be displayed with WR(0) going high andDATA(j) signals containing the analog voltages corresponding to thedesired output light power from each sub-pixel in the first row ofsub-pixels in LED array 33. Just prior to WR(0) going high, WR(200) wenthigh with all DATA(j) signals shorted to VDD to turn off all LEDs in allsub-pixels in row 200. The box labeled “black” and shown in snapshot 60at T0 between WR(0) and WR(200), at T1 between WR(540) and WR(740), atT2 between WR(1080) and WR(1280) and at T3 between WR(1620) andWR(1820), represent a region of display 11 that is emitting no light. Itis in this region, which repetitively travels down display 11 as shown,that spot 14 is detected. At T0, frame N−1 is still displayed below thedark region starting with row 201.

Time T1 occurs one quarter of a frame period after the start of frame Nat which time only the top 25% of frame N is displayed. WR(740) wenthigh to clear another line of frame N−1 and WR(540) went high to displayanother line of frame N. At time T2, the top half frame N is displayedwith WR(1080) going high to display another line of frame N and withWR(1280) going high to clear another line of frame N−1. At time T3,three quarters of frame N is displayed with WR(1620) going high todisplay another line of frame N and with WR (1820) going high to clearanother line of frame N−1.

The timing diagram 61 illustrates the state of the write and sensesignal pairs WR(0) and SNS(0), WR(540) and SNS(270), WR(1080) andSNS(540), and WR(1280) and SNS(640) as a function of time over two frameperiods, N and N+1. As shown in FIG. 4, each pixel 40 has 2 input writesignals WR(i) and WR(i+1) and one input sense signal SNS(i/2). Detailedtiming diagram 62 expands the region in time from T2 when WR(1280)clears a line of frame N−1 to the time when WR(1280) goes low again todisplay another line of frame N.

At time T4 in detailed timing diagram 62, WR(1280) goes low while allDATA(j) signals are high, which turns the light off from any sub-pixelin row 1280 by discharging capacitor 55 and turning transistor 50 off.The voltages across the red LEDs in the red sub-pixels 41 connected toWR(1280) prior to WR(1280) going high is determined by the currentssourced by transistor 50 in each of the red sub-pixels 41 and can beanywhere from 0 to 2 or 3 volts. Detailed timing diagram 62 illustratesthe voltage across one particular red LED that is illuminated by spot14. Prior to WR(1280) going high, Vled(1280,j) can be anywhere from 0 to2 or 3v. When WR(1280) goes high, the voltage relatively slowly driftstowards and intermediate value determined by the optical power of spot14.

At time T5, WR(1280) returns high and WR(1080) goes low with the DATA(j)being driven by column driver 31 with the analog voltages to beprogrammed into the sub-pixels in row 1080. At time T6, WR(1282) goeslow with all DATA(j) signals high, which turns off the current to all ofthe red sub-pixels 41, in the next row of pixels 40 below the rowconnected to WR(1280). Detailed timing diagram 62 also illustrates thevoltage across the red LED in a particular red sub-pixel 41 connected toWR(1282) that is not illuminated by spot 14. Vled(1282,j) goes lowshortly after WR(1282) goes high. At time T7, sense signal SNS(640),which is connected to the same row of pixels 40 as WR(1280), goes low.This turns comparator 45 on, which compares Vled(1280,j) to thereference voltage Vr. Since Vled(1280,j) is at an intermediate voltageand assuming Vr is properly set below this intermediate voltage, SOUT(j)from current sense 34 goes high. At time T8, SNS(640) goes high andSNS(641) goes low, which turns comparator 45 off in the pixel 40 rowconnected to WR(1280) and on in the pixel row 40 connected to WR(1282).Vled(1282,j) is compared to Vr and since Vled(1282,j) is low, SOUT(j)will go low.

At time T9, WR(1280) goes low again, but this time with the DATA(j)signals driven to levels by column driver 31 appropriate to display thered sub-pixel 41 and the white sub-pixel 44 in the 640^(th) line of theimage in frame N. Vled(1280,j) changes accordingly. At time T10,WR(1282) goes low with the DATA(j) signals driven to levels by columndriver 31 appropriate to display the red sub-pixel 41 and the whitesub-pixel 44 in the 641^(st) line of the image in frame N. Vled(1282,j)changes accordingly.

The time between WR(1280) going low the first time at T4 and the secondtime at T9 is equal to the time it takes to display 100 pixel 40 rows ofthe image in frame N. Since this example illustrates the timing for anHD display with 1080 rows, the time from T4 to T9 is equal to about 10%of the frame period. At a 60 Hz frame rate, this time is about 1.7 mSec,which is sufficient for Vled(1280,K) to reach its final value.

Timing diagram 61 and detailed timing diagram 62 only show a smallsubset of the signals in an OLED display 11 since there are thousands ofsuch signals. In particular WR(1281) is not shown since it is notconnected to a red sub-pixel 41 and therefore not involved is detectingspot 14.

FIG. 6 illustrates one of many possibilities for OLED display 11 timing.Since the block and circuit diagrams could be substantially differentfrom FIGS. 3, 4, and 5, the associated signals could be substantiallydifferent from those shown in FIG. 6 and consequently the timingdiagrams would be completely different. For the block and circuitdiagrams shown in FIGS. 3, 4, and 5, the timing shown in FIG. could alsobe significantly different. For instance, the time from T4 to T9 couldshorter or much longer, or the sequencing of the WR(i) signals couldclear multiple lines of the previous frame and then write multiple linesof the current frame.

FIG. 7 is an example architectural diagram for display 11 that usesconventional discreet semiconductor LEDs, which comprises an array LEDdriver ICs 70 with associated LEDs 71 connected serially to each otherand to a network interface (I/F) IC 72. Network interface IC 72 connectsto graphics controller 73 through control and data busses. The array inthis example has N columns and M rows of driver ICs 70 each connected toP LEDs 71. With P equal to 16 and three LEDs per pixel, N and M wouldequal 120 and 3240 respectively for an HD display with 1920×1080resolution. For a standard 48 foot by 14 foot bill board with 3 LEDs perpixel, and P equal to 16, N would equal 48 and M would equal 672.

LED's 71 could all be the same color or could be divided between red,green, and blue for instance. For an RGB display, the different colorscould be arranged in different ways. One example is to organize thedisplay in groups of 3 rows with each row in each group being adifferent color.

Graphics controller 73 produces the data to be displayed digitally,which is forwarded to network interface IC 72. Network interface IC 72serializes the data, which is sent through the chain driver ICs 70 in atime division multiplexed data frame. Each driver IC is assignedspecific time slots from which image data is received and informationabout spot 14 is sent. The data frame repeats at the video frame rate,which enables each driver IC 70 to update the drive current to each LED71 and to report the presence of spot 14 to graphics controller 73 everyvideo frame. Graphics controller 73 processes the responses from alldriver ICs 72 to determine the precise spot 14 location and takes theappropriate action.

FIG. 7 is one of many possible architectural diagrams. For instance,each driver IC 70 could be connected directly to graphics controller 73through a multiplexer either serially or in parallel. The LED driverscould be made from discreet components instead of driver IC 70. The datafor the LED drivers could even be communicated with analog voltagesinstead of digital values.

FIG. 8 is an example block diagram for driver IC 70, which in thisexample drives sixteen LEDs 71 and comprises network interface 81,timing and control circuitry 82, sixteen output drivers 84, digital toanalog converter (DAC) 85, buffer amplifier 86, and current bias 87.Timing and control circuitry 82 further comprises register 83. Outputdriver 84 further comprises pulse width modulator 89, current source 90,and comparator 88.

Network interface 81 accepts serial input data from upstream andproduces serial data for downstream driver ICs 70 as shown in FIG. 7.Network interface 81 further recovers the clock (CK) from the data, anddetects and synchronizes to the input data frame timing. Most receivedserial data is retransmitted, however, data in the assigned timeslotsare forwarded to timing and control circuitry 82. Information about thepresence or absence of spot 14 among other things is produced by timingand control circuitry 82 and forwarded to network interface 81 fortransmission in the assigned timeslots from which LED 71 illuminationdata was removed.

Timing and control circuitry 82 manages the functionality of driver IC70. Illumination data for LEDs 71 is buffered, processed, delayed, andforwarded at the appropriate time to the sixteen output drivers 84.Timing and control circuitry 82 also provides the appropriate digitalvalues at the appropriate times for DAC 85 to produce, together withbuffer 86 and ibias 87, the voltage reference signal VREF and the biascurrent IBIAS used by comparator 88 and current source 90 respectively.Register 83 is also clocked at the appropriate time by the capture (CAP)signal to store the sixteen comparator 88 outputs (CMP).

Output driver 84 produces pulse width modulated current to LED 71 andmonitors the LED 71 voltage induced by incident light from spot 14 forinstance. Modulator 89 receives a digital number from timing and controlcircuitry 82 and produces a logic level signal (PWM) that turns currentsource 90 on and off. The frequency of PWM is typically equal to theserial data frame and the video frame rate with the duty cycle relatedto the digital value from timing and control circuitry 82. Currentsource 90 produces current proportional to IBIAS during the time thatPWM is high that is drawn through LED 71 to produce light.

The maximum duty cycle of PWM is set by the maximum value of the numberfrom timing and control circuitry 82, and is typically some fraction ofa video frame period, for instance one quarter. Once this maximum amountof time has passed from the start of a pulse on PWM, timing and controlcircuitry 82 changes the value provided to DAC 85 to produce VREF andgenerates a pulse on CAP to store the sixteen comparator 88 outputs inregister 83 some time later. If spot 14, for instance, is illuminatingone of the LEDs 71, that LED 71 will generate a voltage that is greaterthan VREF, which causes the CMP output from the associated comparator 88to go high. An LED 71 that is not illuminated will not generate avoltage greater than VREF, which will cause the CMP output from theassociated comparator 88 to be low.

FIG. 8 is just one example of many possible driver IC 70 block diagrams.For instance, network interface 81 would not be needed if each driver IC70 in FIG. 7 were directly connected to graphics controller 73. With theserial configuration shown in FIG. 7, network interface 81 would notneed to recover a clock from data if another input was used to accept aclock input. Likewise, if a frame clock input was provided, networkinterface 81 would not need to synchronize to the serial input frametiming. Additionally, each output driver 84 could include a current DACinstead of modulator 89 and current source 90. Such a DAC would providea variable amount of current for a fixed amount of time instead of afixed current for a variable amount of time. Also spot 14 could bedetected by measuring the LED 71 current induced by spot 14 instead ofLED 71 voltage.

FIG. 9 illustrates an example for the timing of an LED display 11 usingconventional discreet semiconductor LEDs, which includes snapshots 91and timing diagram 92. Snapshots 91 illustrate the state of display 11at four different times, T0, T1, T2, and T3 within one video frame N.The region labeled “frame n” of each snapshot represents the image andthe region labeled “black” of each snapshot represents rows that are notproducing light. For example, at T0 only rows 1 to M/4 are producinglight; at T1 only rows M/4 to M/2 are producing light, at T2 only rowsM/2 to 3M/4 are producing light, and at T3 only rows 3M/4 to m areproducing light.

Time T0 occurs one quarter of the way through frame N with the top onequarter of the image displayed. At T0 all the PWM signals in all driverICs 70 in the M/4^(th) row are just turning on and all the PWM signalsin all the driver ICs 70 in the first row are guaranteed to be off. Mostof the PWM signals in the first row will be off before T0 due tomodulated brightness, but T0 is the first time all PWM signals in suchrow are guaranteed to be off.

Time T1 occurs one half of the way through frame N with the secondquarter of the image displayed from row M/4 to M/2. Time T2 occurs threequarters of the way through frame N with the third quarter of the imagedisplayed. Time T3 occurs at the end of frame N with the bottom quarterof the image displayed. At times between those that the snapshots 91represent, one quarter of the image will be displayed in this example,but will be located at different positions on the display 11. Thequarter displayed progresses from the top of the display to the bottomduring a frame period.

Timing diagram 92 illustrates possible timing of PWM and CAP signals indriver ICs 70 in four different rows, 1, M/4, M/2, and 3M/4, which arelocated at the top, and one quarter, one half, and three quarters of theway down display 11. The index J indicates all columns in such row. Attime T4, which is the beginning of frame N, the PWM signals in the firstrow of driver ICs 70 turn on. By T0 all such signals are guaranteed tobe off. At time T5, which is equally far apart from T0 and the end offrame N at T3, the CAP signals in all driver ICs 70 in the first row arepulsed to capture the CMP signals output from comparators 88. Suchtiming of CAP relative to PWM minimizes optical coupling from LEDs thatare on from interfering with spot 14 detection.

Times T6, T7, and T8 illustrate possible times to pulse CAP in driverICs 70 one quarter, one half, and three quarters of the way down display11. The pulse on the CAP signals progresses down display 11 followingthe section of the image being displayed by three eighths of thedisplay.

FIG. 9 illustrates one of many possible LED display diagrams. Forinstance, the amount of time LEDs 71 in any one are off can besubstantially shorter or longer, and the time when LEDs 71 are sampledfor spot 14 detection can vary as well. Rows as well columns can also bescanned so that only one driver IC 70 turns on at a time, instead of anentire row. Display 11 can be scanned on a column basis instead of a rowbasis, or not at all. The entire image can be flashed on and then off.If driver IC 70 uses variable current for fixed amounts of time insteadof fixed current for variable amounts of time the PWM signals thatenable the current to LEDs 71 would all be high for a fixed amount oftime instead of a variable amount as shown in timing diagram 92.

FIG. 10 illustrates an example timing diagram for the signals within onedriver IC 70 located in a row near the top of display 11, which ispartially illuminated by spot 14. In this example driver IC 70 has 16output drivers 84 connected to sixteen LEDs 71. The first LED 71 isilluminated by spot 14 and the sixteenth is not. At time T0, frame Nbegins. At time T1, the PWM signals go active. At time T2, all PWMsignals are guaranteed to be low and the current sources 90 areguaranteed to be off. The VLED(1) signal associated with the first LED71 and output driver 84 in driver IC 70, which is illuminated by spot 14moves towards the voltage induced by the incident light. VLED(16) simplygoes high since the associated LED 71 is not illuminated.

At time T3, timing and control circuitry 82 loads DAC 85 with theappropriate value for VREF. By the time T4, all VLED signals and VREFhave stabilized. CAP is pulsed by timing and control circuitry 82 andcomparator 88 outputs CMP are sampled. Such information is communicatedto graphics controller 73, which determines spot 14 location and takesthe appropriate action.

FIG. 10 is just one example of many possible driver IC 70 timingdiagrams. Output driver 84 may not have a pulse width modulator, so thePWM signals would be different. The time that CAP is pulsed could bedifferent and does not necessarily need to exist. If comparator 88 isreplaced by analog to digital converter (ADC), the stream of digitalsample values can be analyzed by a processor. VREF could be a fixedvalue or a variable value controlled by a dedicated DAC.

FIG. 11 is an example block diagram of display 11 implemented with aliquid crystal display (LCD) and an LED backlight, which comprises LCDarray 100, LED array 101, graphics and timing controller 102, row driver103, column driver 104, and backlight driver network 105. In thisexample, LCD array 100 has R rows and C columns of elements with rowdriver 103 producing R number of WR signals and column driver 104producing C number of DATA signals. Graphics and timing controlcircuitry 102 provide data and timing to both row driver 103 and columndriver 104 in a similar manner to an OLED display as described in FIG.3.

In this example, LED array 101 comprises M rows and N columns of LEDsdriven by backlight driver network 105, which comprises a number of LEDdriver ICs connected together as in the LED display illustrated in FIG.7. LCD array 100 comprises pixel elements that control the amount oflight that can pass through. LED array 101 produces the light that isselectively passed through LCD array 100. Both LCD array 100 and LEDarray 101 can be scanned to minimize motion blur. Between frames, allelements of LED array 101 are turned off and all elements of LCD array100 are made transparent so that spot 14 can be detected by LED array101 in combination with backlight driver network 105 and graphics andtiming control circuitry 102.

FIG. 11 is just one of many possible block diagrams for display 11 basedon LCD and LED backlighting technology. For instance, all LED elementsin LED array 101 could be directly connected to graphics and timingcontrol circuitry 102 through a multiplexer instead of backlight drivernetwork 105.

FIG. 12 is an example circuit diagram for the LCD pixel element in LCDarray 100 and the associated row driver 103 and column driver 104, whichcomprises transistor 120, capacitor 121, liquid crystal 122, bufferamplifier 123, and inverter 124. Such pixel element is repeatedhorizontally C times and vertically R times to produce LCD array 100,with each row of pixel elements controlled by a WR signal from aninverter 124 in row driver 103 and each column of pixel elementsconnected to a single DATA signal from buffer amplifier 123 in columndriver 104.

The transparency of liquid crystal 122 is controlled by the voltageacross capacitor 121, which is set by driving DATA(j) with the desiredvoltage and then pulsing WR(i) high to make transistor 120 conductive.When WR(i) is high, capacitor 121 is charged to the voltage on DATA(J),which is driven by buffer amplifier 123.

FIG. 12 is just one of many possible LCD array 100, row driver 103, andcolumn driver 104 circuit diagrams. For instance, some pixel elementscontain multiple transistor to compensate for transistor 120 variationsand speed up the write process.

FIG. 13 is an example illustration of display 11 timing for a 60 Hz HighDefinition (HD) TV with 1080 rows of pixels, which shows how the imageand backlight are scanned, and spot 14 is detected. The backlight inthis example comprises 64 rows of LEDs 71. FIG. 13 includes sevensnapshots 130 of display 11 at times T1, T2, T3, T4, T5, T6, and T7within one frame period. Below the snapshots 130 is timing diagram 131for the WR signals to LCD array 100 and the PWM signals in driver IC 70in backlight driver network 105. Below timing diagram 131 is detailedtiming diagram 132 that illustrates the last ten percent of a frame,which is when spot 14 is detected, in expanded detail. Detailed timingdiagram 132 illustrates the signals inside driver IC 70 for an LED 71that is illuminated by spot 14, VLED(1), and for an LED 71 that is notilluminated, VLED(16).

A frame starts at time T0, with image data written to the top row of LCDarray 100 by WR(1) pulsed high. At time T1, as shown in snapshots 130, atop portion of display 11 represented by the region labeled “loaded” hasbeen loaded with image data, and a bottom portion represented by theregion labeled “black” has not been loaded with image data. At times T2through T5, the regions labeled “loaded” also represent regions thathave been loaded with image data, and the regions labeled “black” alsorepresent regions that have not been loaded with data. At time T1, thefirst row of the LED array 101 is also turned on by PWM(1,j) going high.The index J represents all the PWM signals in a row, which in this caseis the first row. The time from T0 to T1 represented by Tdly is 3.3 mSecin this example and is typically necessary for liquid crystal 122 tostabilize after being written and before being illuminated by LEDs 71.

At time T2, WR(540) is pulsed high, which indicates that the top half ofthe image has been loaded into LCD array 100. At this time the LEDs 71in the first row of LED array 101 are also turned off as PWM(1,j) goeslow. The offset non-labeled box in snapshots 130 at times T2 through T5represents the region of the LED array 101 that is emitting light. Thebox is offset to represent that these rows are also loaded with imagedata. The time from T1 to T2 represented by Tbl is 1.7 mSec in thisexample and is the length of time each row of LED array 101 is turnedon.

At time T3, the illuminated region of LED array 101 reaches the centerof display 11 with PWM(32,j) going high. At time T4, the last row of LCDarray 100 is loaded with data completing the image scan, which began attime T0. The time between T0 and T4 represented by Tscn is 10 mSec inthis example. After an additional Tdly of 3.3 mSec, the illuminatedregion of LED array 100 reaches the bottom of display 11 with PWM(64,j)going high at time T5. After another Tbl time of 1.7 mSec, LED array 101is completely turned off with PWM(64,j) going low at time T6.

At time T6, all pixel elements of LCD array 100 are configured to betransparent by setting all DATA signals to the level that makes liquidcrystal 122 transparent, which is high in this example, andsimultaneously pulsing all WR signals. While LCD array 100 is clear,spot 14 can be detected by backlight driver network 105. Aftersufficient time for such detection, LCD array 100 is made opaque at timeT7 by setting all DATA signals to the level that makes liquid crystal122 opaque, which is low in this example, and simultaneously pulsing allWR signals a second time.

Detailed timing diagram 132 is an expanded version of the time from T6to T7 and shows the relevant signals of driver IC 70 for detecting spot14. Just prior to T6, PWM(64,j) goes low, which turns LED array 100completely off. At T6, all WR signals represented by WR(1:1080) pulseswhile all DATA signals represented by DATA(1:5760) are high, whichclears LCD array 100. There are 5760 DATA signals in this example, whichprovides 1920 signals for each color component. At time T6, the voltageacross the LED 71 that is illuminated by spot 14, which is representedby signal VLED(1) begins to drift toward an intermediate level, whilethe voltage of signal VLED connected to an LED 71 that is notilluminated, which is represented by VLED(16), goes high since LED 71 isconnected to VDD.

At time T8, timing and control circuitry 82 in every driver IC 70 inbacklight driver network 105 updates DAC 85 with the appropriate valueto generate a proper Vref. Vref in all driver ICs 70 is represented byVreg(1,j). Some time after Vref is properly set, CMP(16) stabilizes at alow level indicating no spot 14 and CMP(1) stabilizes at a high levelindicating the presence of spot 14. At time T9, the CAP signal in alldriver ICs 70 in backlight driver network 105 represented by CAP(i,j)pulses, which stores the state of the CMP signals in register 83. Suchspot 14 information is communicated to graphics and timing controlcircuitry 102, which takes the appropriate action. At time T7, all WRsignals represented by WR(1:1080) pulse while all DATA signalsrepresented by DATA(1:5760) are low, which makes LCD array 100 opaque inthis example. The time from T6 to the end of the frame can be anadditional Tsns of 1.7 mSec.

FIG. 13 illustrates just one of many possible timing diagrams fordisplay 11 built using LCD with LED backlighting technology. LCD array100 and LED array 101 can be scanned many different ways. Additionally,LED array 101 may be flashed instead of scanned, with all flashes beingthe same color or sequenced through the color components, such as red,green, and blue. The timing diagrams for the different scanning orflashing methods could be substantially different from FIG. 13.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Second Embodiment

Display calibration systems and related methods are also disclosed thatuse the photo-sensitivity of LEDs to correct for variations between LEDsduring initial production and over lifetime for display systems. Variousembodiments are described with respect to the drawings below. Otherfeatures and variations can also be implemented, if desired, and relatedsystems and methods can be utilized, as well.

In part, the disclosed embodiments relate to displays including arraysof LEDs that use the photo-sensitivity of the LEDs to correct forvariations between LEDs during initial production and over lifetime ofsuch a display. Such LED arrays can produce images directly as in LEDbillboards and sports arena scoreboards, and smaller Organic LED (OLED)displays, or can produce the backlight for LCD screens for instance.Variations in LED brightness and color can be compensated for in orderfor such a display to have uniform color and brightness. Suchcompensation, which is typically done in prior systems by measuring theoptical output power of each individual LED or purchasing speciallytested LEDs, is performed in the embodiments described below by simplymeasuring the signal induced on each LED by uniform incident light.

In one improved embodiment, the system infers the optical output powerand optionally also the peak wavelength produced by each LED in an LEDarray for LED billboards and stadium displays for instance, or LCDbacklighting, by measuring the photo-sensitivity of each such LED,comparing such sensitivity to the photo-sensitivity of the other LEDs insuch array, and adjusting such LED drive current correction factorsaccordingly. Such correction factors can be initially generated duringproduction of such LED array by measuring each such LED optical outputpower and peak wavelength directly, for instance, or by inferring eachsuch LED optical output power and peak wavelength from photo-sensitivityand other measurements.

LEDs not only produce light with a specific peak wavelength when forwardbiased, but also forward bias when illuminated with light at or abovesuch peak wavelength. The electrical power produced by a fixed incidentoptical power decreases with decreasing incident wavelength with themaximum power produced by incident light with a wavelength near suchpeak emission wavelength. Incident wavelengths above such peak emissionwavelength produce roughly no electrical power in such LED. At aspecific temperature, the relationship between voltage and currentinduced across a properly illuminated LED depends on the amount ofillumination, the bandgap voltage of the semiconductor, and theresistive load placed across the LED. As the bandgap voltage of thesemiconductor increases, the open circuit voltage (Voc) increases andthe short circuit current (Isc) decreases. Since peak emissionwavelength decreases with increasing bandgap voltage, the ratio of Vocto Isc can be measured to get an indication of wavelength variationsbetween LEDs in an LED array.

The amount of light produced by different LEDs within a manufacturinglot or between lots when driven with a fixed current varies primarilydue to differences in the optical path, such as transparency oralignment, and differences in the extent of imperfections in thestructure of the light emitting region of the LED. Likewise, suchdifferences similarly affect the photo-sensitivity of such LED whenproperly illuminated. Consequently, photo-sensitivity parameters, suchas Voc and Isc, can be monitored to infer the amount of light that suchLED will produce when driven with current.

Wavelength and output power from individual LEDs in an LED array can becompensated by correction coefficients to produce uniform intensity andcolor across such an array. Such correction coefficients determinedduring manufacturing of such an LED array by the methods describedabove, by directly measuring the intensity and wavelength of the lightproduced by each LED, or any other method, can be stored in memory insuch a display. Likewise, photo-sensitivity parameters, such as Voc andIsc, produced in response to a light source with fixed parameters, canalso be stored in such memory. Periodically, during the life of such adisplay, the LED array can be illuminated with a light source with thesame or different parameters as the initial light source, thephoto-sensitivity parameters can be measured, and differences betweenthe initial and new photo-sensitivity parameter values can be used tomodify the correction coefficients to correct for any additional shiftin illumination from LEDs in such an LED array.

The light source used to calibrate an LED array during initialproduction can be direct or diffuse sunlight, a lamp that mimics thespectrum of sunlight, or any light source with a spectrum sufficient togenerate reliably measurable photo-sensitivity parameters from LEDs ofeach color. To re-calibrate a large LED billboard or stadium display,for instance, the same light source with the same intensity can be usedto measure the photo-sensitivity parameters under the exact samecondition as when such a display was manufactured. Any shift in anyphoto-sensitivity parameter can be used directly to update correspondingcorrection coefficients. If precisely controlling the light sourceintensity is not possible, then comparing changes in one LED relative tothe others enables uniform display intensity and color to be recreated.The user could simply manually adjust overall brightness.

For consumer devices such as an LCD television, calibration with aprecise light source may not be possible. A close approximation could bediffuse sunlight, but the spectrum of sunlight varies with time day andyear, and location. Additionally, such a device could be in an enclosedroom with artificial lighting. In such a case, uniformity across LEDs ofeach color component can be produced, but the relative intensity betweencolor components may not. The user in this case could manually adjustboth overall brightness and hue to the desired levels.

The improved display calibration systems and related methods describedherein address calibration issues for displays using arrays of LEDsdirectly or as backlights for illumination. And the calibration systemsand related methods described herein greatly reduce or eliminate theneed for teams of specially trained and equipped people to keep LEDbillboards and stadium displays calibrated during operation over time.

As stated above, this second embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to this embodiment can beused within the other described embodiments, as desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to calibration and detection systems and methodsdescribed in this second embodiment, as desired. Further, as statedabove, the structures, techniques, systems and methods described withrespect to this second embodiment can be used in the other embodimentsdescribed herein, and can be used in any desired lighting relatedapplication, including liquid crystal displays (LCDs), LCD backlights,digital billboards, organic LED displays, AMOLED (Active Matrix OLED)displays, LED lamps, lighting systems, lights within conventional socketconnections, projection systems, portable projectors and/or otherdisplay, light or lighting related applications.

Turning now to the drawings, FIG. 14 is one example of displaycalibration system 1410 that comprises the display 1411 and light source1414. Display 1411 comprises an array of light emitting diodes (LEDs)arranged as pixels 1412 for image illumination either directly in thecase of OLED or conventional LED displays, or backlighting in the caseof Liquid Crystal Displays (LCDs). Pixel 1412 preferentially comprisesdifferent color sub-pixels 1413, for instance red, green, and blue, toproduce the wide gamut of colors typically necessary for accuraterepresentation of images either directly in the case of OLED or LEDdisplays, or modulated as in an LCD. Sub-pixel 1413 comprises an LED.

Light source 1414 can be direct or diffuse sunlight, or artificial lightfrom a lamp with a precise emitted light spectrum. During themanufacturing of display 1411, light source 1414 illuminates display1411 uniformly to calibrate the intensity and wavelength of lightemitted from each pixel 1412 and to measure and store photo-sensitivityparameters such as Voc and Isc, or to simply measure and storephoto-sensitivity parameters in which case the intensity and wavelengthof all pixels 1412 are calibrated by some other means such as measuringthe light produced by each such pixel and adjusting some compensationcoefficients accordingly. After some period of use, preferentially thesame light source 1414 again illuminates display 1411 and thephoto-sensitivity parameters of the LED comprising each sub-pixel 1413,such as Voc and Isc, are again measured and preferentially compared tothose stored during the manufacturing of such display 1411. Any shift insuch photo-sensitivity parameters or preferentially any difference inshift of such parameters in one pixel 1412 relative to preferentiallythe average shift in all pixels 1412 causes such compensationcoefficients to be adjusted inversely proportional in such one pixel1412.

If the Isc of the LED comprising a red sub-pixel 1413 for instance,decreases by more than the average decrease of all red sub-pixels 1413,such red sub-pixel compensation coefficients are increased to producemore current to such red sub-pixel 1413 by an amount preferentiallyinversely proportional to the percentage difference in the Isc changebetween such red sub-pixel 1413 and the average Isc change from all redsub-pixels 1413 in display 1411. Since the intensity of illumination ondisplay 1411 from light source 1414 is relatively difficult to controlfrom manufacturing time to such re-calibration time, any change incompensation coefficients for red sub-pixels 1413 for instance, ispreferentially normalized to the average Isc from all red sub-pixels1413.

FIG. 14 is one example of many possible display calibration systems1410. For example, pixel 1412 could comprise more or less sub-pixels1413 and such sub-pixels 1413 could comprise more or less differentcolored LEDs including just one color. Display 1411 could be an LCD, anOLED display, or a conventional LED display or just portions of suchdisplays. Light source 1414 could be a single light source or many lightsources with the same or different spectrums.

FIG. 15 is an example block diagram of OLED display 1411 comprising LEDarray 1523 with R rows and C columns of sub-pixels 1413 typicallyarranged in pixels 1412 of one red, one green, one blue, and one whitesub-pixel LED. LED array 1523 comprises R/2 rows and C/2 columns of suchsub-pixels 1413. Each sub-pixel 1413 is configured to produce a certainamount of light by a combination of voltages on a particular WR (write)signal produced by row driver 1522 and DATA signal produced by columndriver 1521. When a WR signal is high, the analog voltage on each DATAsignal is programmed into the row of sub-pixels 1413 activated by theparticular WR signal.

Power supply 1525 produces the main power Vdd and the ground Vg for LEDarray 1523. The voltage on such Vg signal is equal to zero volts duringnormal operation and during the Voc measurement of each sub-pixel 1413,and is elevated slightly above display 1411 ground during Iscmeasurements.

During calibration, graphics and timing control circuitry 1520 sequencesrow driver 1522 through rows of LED array 1523 by pulsing each SNS(sense) signal high. When one of the SNS signals from row driver 1522goes high, the IVOUT signals from the LED array 1523 source current orvoltage into IV sense 1524 for sub-pixels 1413 in the row activated by aparticular SNS signal. Depending on the state of the voltage mode enablesignal Ven, IV sense 1524 either will pass the voltages on the IVOUTsignals to ADC 1526 or will short the IVOUT signals to Vg, convert theresulting currents to voltages, and forward the resulting voltages toADC 1526. ADC 1526 together with timing information from graphics andtiming control circuitry 1520 sequentially converts the voltagesforwarded by IV sense 1524 to digital values, which are forwarded tographics and timing control circuitry. 1520 for processing.

Graphics and timing control circuitry 1520 can receive Voc and Isc, andother calibration information from sub-pixels 1413, and can compare suchinformation with previously stored such values to determine any changesnecessary to correction coefficients. Graphics and timing controlcircuitry 1520 can use such correction coefficients to adjust thevoltages programmed into sub-pixels 1413 to compensate for variations inlight output from each sub-pixel 1413 relative to other sub-pixels 1413.

FIG. 15 is just one of many possible block diagrams for display 1411,which could be built using any one of a wide range of technologiesincluding but not limited to discreet inorganic LED arrays or liquidcrystals. Likewise, the block diagram for display 1411 built with OLEDscould be substantially different. For instance, with additionallycircuitry in sub-pixels 1413, the SNS signals or the IVOUT signals couldbe eliminated, by using the WR and DATA signals during calibration.Additionally, the Vg could simply be system ground provided N sense 1524circuitry was different.

FIG. 16 is an example block diagram of OLED pixel 1412 in LED array 1523referenced by row coordinates I and I+1, and column coordinates J andJ+1, and comprising red, green, blue, and white sub-pixels 1413. Thecircuitry in all sub-pixels is the same except the color of the includedLED.

Signals WR(i) and DATA(j) program the light produced by red sub-pixel1413, signals WR(i) and DATA(j+1) program the light produced by whitesub-pixel 1413, signals WR(i+1) and DATA(j) program the light producedby green sub-pixel 1413, and signals WR(i+1) and DATA(j+1) program thelight produced by blue sub-pixel 1413. All sub-pixels are powered by thevoltage difference between Vdd and Vg.

FIG. 16 is just one of many possible pixel 1412 block diagrams. Forinstance, any combinations of colors or just one color could be used.Additionally, all sub-pixels could be accessed by one WR signal and oneDATA signal if two enable signals select between the sub-pixels.

FIG. 17 is an example circuit diagram for sub-pixel 1413 and anindividual current and voltage sense element in IV sense 1524 referencedby coordinate J. When producing light, LED 1744 is driven by the currentthrough transistor 1740, which is set by the voltage stored on capacitor1743 and the gate of transistor 1740. The voltage on capacitor 1743 isset to the voltage on DATA(j) signal when WR(i) signal is low. WhenWR(i) goes high, capacitor 1743 holds the voltage so that DATA(j) can beused to program the current in other rows of sub-pixels 1413 when otherWR signals go low. All the sub-pixels 1413 connected to WR(i) areprogrammed simultaneously by all the DATA signals when WR(i) is low.

When SNS(i) goes high, the Voc and Isc induced across LED 1744 byincident light can be measured by IV sense 1524, after capacitor 1743 isdischarged by setting WR(i) low and DATA(j) high. Voc is measured whengraphics and timing control circuitry 1520 sets the Ven signal high,which tri-states the output of amplifier 1746 and causes power supply1525 to hold Vg at zero volts. The voltage on IVOUT(j) passes throughresistor 1745 and to the high impedance input of ADC 1526, whichconverts such voltage to a digital value and forwards such value tographics and timing control circuitry 1520.

Isc is measured when graphics and timing control circuitry 1520 sets theVen signal low, which enables amplifier 1746 and forces the voltage onIVOUT(j) to the voltage on Vg. The resulting current flows throughresistor 1745 producing a voltage on Sout(j) proportional to the Iscinduced on LED 1744 by incident light. Since the voltage on Sout(j) islower than that on Vg and IVOUT(j), the negative supply for IV sense1524 and ADC 1526 is set to be lower than Vg. Power supply 1525 canraise the voltage on Vg to some small voltage, such as one volt abovethe negative supply, for instance ground, for display 1411.

Although not associated with photo-sensitivity of LED 1744,characteristics of transistor 1740 can be measured by such sub-pixel1413, IV sense 1524, and ADC 1526 circuitry, and compensated by graphicsand timing control circuitry 1520. After a voltage is programmed acrosscapacitor 1743, the corresponding current produced by transistor 1740can be measured when SNS(i) high and Ven is low. The voltage on IVOUT(j)is forced to the voltage on Vg by amplifier 1746 and resistor 1745 withthe resulting current flowing through resistor 1745, which produces avoltage on SOUT(j) proportional to transistor 1740 current. Such voltagecan be digitized by ADC 1526 and processed by graphics and timingcontrol circuitry 1520, which can compensate for variations betweentransistors 1740 in all sub-pixels 1413.

FIG. 17 is one of many possible circuit diagrams for sub-pixels 1413 andIV sense 1524. For instance, sub-pixel 1413 could include additionalcircuitry to compensate for transistor 1740 variations without involvinggraphics and timing control circuitry 1520. Additionally, to detect LED1744 Voc and Isc in response to incident light, sub-pixel 1413 couldinclude more complex circuitry to buffer such signals prior to leavingsuch sub-pixel 1413.

FIG. 18 is an example architectural diagram for display 1411 that usesconventional discreet semiconductor LEDs, which comprises an array ofLED driver ICs 1850 with associated LEDs 1851 connected serially to eachother and to a network interface (I/F) IC 1852. Network interface IC1852 connects to graphics controller 1853 through control and databusses. The array in this example has N columns and M rows of driver ICs1850 each connected to P LEDs 1851. With P equal to 16 and three LEDsper pixel, N and M would equal 120 and 3240 respectively for an HDdisplay with 1920×1080 resolution. For a standard 48 foot by 14 footbill board with 3 LEDs per pixel, and P equal to 16, N would equal 48and M would equal 672.

LED's 1851 could all be the same color or could be divided between red,green, and blue for instance. For an RGB display, the different colorscould be arranged in different ways. One example is to organize thedisplay in groups of 3 rows with each row in each group being adifferent color.

Graphics controller 1853 produces the data to be displayed digitally,which is forwarded to network interface IC 1852. Network interface IC1852 serializes the data, which is sent through the chain of driver ICs1850 in a time division multiplexed data frame. Each driver IC 1850 isassigned specific time slots from which image data is received andcalibration information can be sent. The data frame repeats at the videoframe rate, which enables each driver IC 1850 to update the drivecurrent to each LED 1851.

Driver IC 1850 can further process the data to be displayed withcorrection coefficients that adjust the drive current to each LED 1851such that brightness and color are uniform across display 1411. Suchcorrection coefficients can be stored in graphics controller 1853,downloaded through network interface IC 1852 to driver ICs 1850 eachtime display 1411 is turned on, and updated periodically by graphicscontroller 1853. Such correction coefficients can be created and updatedperiodically over the life of display 1411 by graphics controller 1853using individual LED photo-sensitivity parameters such Voc and Iscmeasured by driver ICs 1850 on commands from graphics controller 1853,for instance.

FIG. 18 is one of many possible architectural diagrams. For instance,each driver IC 1850 could be connected directly to graphics controller1853 through a multiplexer either serially or in parallel. The LEDdrivers could be made from discreet components instead of driver IC1850. The data for the LED drivers could even be communicated withanalog voltages instead of digital values. Additionally, the creationand updating of correction coefficients could be performed by driver IC1850, or processing of the data to be displayed with correctioncoefficients could be performed by graphics controller 1853 forinstance.

FIG. 19 is an example block diagram for driver IC 1850, which in thisexample drives sixteen LEDs 1851 and comprises network interface 1960,timing and control circuitry 1961, and sixteen output drivers 1964.Timing and control circuitry 1961 further comprises IV sense block 1962and correction matrix 1963. Output driver 1964 further comprises pulsewidth modulator 1965, and current source 1966.

Network interface 1960 accepts serial input data from upstream andproduces serial data for downstream driver ICs 1850 as shown in FIG. 18.Network interface 1960 further recovers the clock (CK) from the data,and detects and synchronizes to the input data frame timing. Mostreceived serial data is retransmitted, however, data in the assignedtimeslots are forwarded to timing and control circuitry 1961.Calibration information, such Voc and Isc, among other things isproduced by timing and control circuitry 1961 and forwarded to networkinterface 1960 for transmission in the assigned timeslots from which LED1851 illumination data was removed.

Timing and control circuitry 1961 manages the functionality of driver IC1850. Illumination data for. LEDs 1851 is buffered, processed, delayed,and forwarded at the appropriate time to the sixteen output drivers1964. Such processing can include among other things adjustment of theillumination data to compensate for variations between LEDs to produceuniform brightness and color across display 1411. Matrix 1963 cancomprise correction coefficients that when combined with theillumination data produce the data forwarded to output drivers 1964,which have pulse width modulators 1965 that produce logic level signalsthat turn current sources 1966 on and off to LEDs 1851. The frequency ofsuch PWM signals is typically equal to the serial data frame rate andthe video frame rate with the duty cycle related to the digital valuefrom matrix 1963.

Timing and control circuitry 1961 has access to both terminals of all16, in this example, LEDs connected to driver IC 1850 through IV senseblock 1962, which among other things can measure Voc and Isc producedacross LEDs 1851 in response to incident light. The anodes of allsixteen LEDs in this example can be tied together to a single supplyvoltage Vd, or can be connected to different supply voltages. In thecase all sixteen LEDs 1851 are of one color, all anodes preferentiallywould be connected together. In the case such sixteen LEDs 1851 are ofdifferent colors, each such different color LED 1851 wouldpreferentially be connected to each such different supply voltage.

FIG. 19 is just one example of many possible driver IC 1850 blockdiagrams. For instance, network interface 1960 would not be needed ifeach driver IC 1850 in FIG. 18 were directly connected to graphicscontroller 1853. With the serial configuration shown in FIG. 18, networkinterface 1960 would not need to recover a clock from data if anotherinput was used to accept a clock input. Likewise, if a frame clock inputwas provided, network interface 1960 would not need to synchronize tothe serial input frame timing. Additionally, the function of matrix 1963could be performed by graphics controller 53, which would eliminate theneed for such matrix 1963 in driver IC 1850. Modulator 1965 would not beneeded if LEDs 1851 were driven with variable current for fixed amountof times, for instance.

FIG. 20 is an example block diagram of correction matrix 1963 that cancorrect for variations in light intensity produced by a pixel 1412comprising red, green, and blue LEDs 1851 to produce relatively uniformbrightness and color across a display 1411. Matrix 1963 comprises memory2070 that can store correction coefficients Cr, Cg, and Cb, which arecombined by multipliers 2071 with the red, green, and blue illuminationdata respectively from graphics controller 1853 to produce theillumination data forwarded to modulators 1965 controlling red, green,and blue LEDs 1851 respectively. Such correction coefficients aretypically relatively large, which produce adjustments in theillumination data to compensate for variations between LEDs 1851.

Memory 2070 can be made from SRAM, DRAM, FLASH, registers, or any otherform of read-writable semiconductor memory. Such correction coefficientsperiodically can be modified by graphics controller 1853, driver IC1850, or any other processing element in display 1411 to adjust forchanges in LED 1851 characteristics for instance over temperature orlifetime. Typically, such correction coefficients are downloaded intomemory 2070 from graphics processor 1853 every time display 1411 isturned on. Such correction coefficients are typically modified tocompensate for LED 1851 aging effects by graphics controller 1853 ordriver IC 1850 after some fixed number of hours of use, after every use,or on demand.

Multipliers 2071 scale the illumination data from graphics controller1853 by multiplying each color component by the corresponding correctioncoefficient. Such multiplication can be performed by discreet hardwarein bit parallel or bit serial form, in an embedded microcontroller, orby any other means. Preferentially, one hardware multiplier comprising ashifter and an adder performs all three multiplications each videoframe. As such, FIG. 20 is just one of many possible block diagrams forcorrection matrix 1963.

FIG. 21 is an example block diagram for correction matrix 1963 that cancorrect for variations in both light intensity and wavelength producedby a pixel 1412 comprising red, green, and blue LEDs 1851 to produceuniform brightness and color across a display 1411. Matrix 1963comprises memory 2070 that can store nine correction coefficients withthree such coefficients for each color component produced. CoefficientsCrr, Cgg, and Cbb would typically be effectively the same as Cr, Cg, andCb from FIG. 20 to adjust for intensity variations in LEDs 1851, whilethe remaining coefficients (Crg, Crb, Cgr, Cgb, Cbr, Cbg) compensate forwavelength variations.

For instance, if the red illumination data from graphics controller 1853was intended for an LED 1851 with a wavelength of 650 nm and theconnected LED 1851 wavelength was exactly 650 nm, coefficients Cgr andCbr would be zero and Crr would be close to one. If such connected LED1851 wavelength was 640 nm and had the same intensity as the justprevious example, Crr would be slightly smaller than in the justprevious example and Cgr and Cbr would be non-zero, which would producesome light from such green and blue LEDs 1851. The wavelength of thecombination of light from such red, green, and blue LEDs 1851 would beperceived the same as mono-chromatic light from a single red LED 1851emitting at precisely 650 nm.

Memory 2070 and multipliers 2071 can operate and be implemented asdescribed for FIG. 20. Adder 2180 sums the multiplication results fromthe three connected multipliers 2071 to produce the illumination dataforwarded to modulators 1965. Such adders 2080 can be implemented inhardware or software, or be performed bit parallel or bit serial.Preferentially, such three adders 2080 are implemented with common bitserial hardware that performs such three additions sequentially eachvideo frame. As such FIG. 21 is just one of many possible intensity andwavelength correction matrix 1963 block diagrams.

FIG. 22 is an example block diagram of IV sense block 1962 in timing andcontrol block 1961 of driver IC 1850, which can measure LED 1851photo-sensitivity parameters, such as Voc and Isc, when current source1966 is off. Following the example in FIG. 18, the anodes of sixteenLEDs 4851 represented by the signals Vled(1:16) are connected tomultiplexer 2294 with one such Vied signal selected to pass through.Such output of multiplexer 2294 is connected to an input of multiplexer2291 and to the negative terminal of amplifier 2292 and resistor 2293.Such multiplexers 2291 and 2294 comprise switches that connect input tooutput and allow current to flow in both directions for the selectedinput. The output of amplifier 2292 is also connected to multiplexer2291 the output of which is connected to analog to digital converter(ADC) 2290.

Amplifier 2292 and resistor 2293 form a trans-impedance amplifier whichforces the anode of the LED 1851 selected by multiplexer 2294 to thesame voltage as signal Vd, which is connected to the positive terminalof amplifier 2292. The resulting current flows through resistor 2293producing a voltage proportional to the selected LED 1851 short circuitcurrent Isc, which can be digitized by ADC 2290 if selected bymultiplexer 2291. Alternatively, the open circuit voltage Voc of the LED1851 selected by multiplexer 2294 can be digitized by ADC 2290 ifmultiplexer 2291 selects such signal. The power supply for IV senseblock 1962 is made to be higher than Vd since the output of amplifier2292 may go higher than Vd.

FIG. 22 is just one of many possible block diagrams for circuitry tomeasure photo-sensitivity parameters of LEDs 1851. For instance, a rangeof LED 1851 current and voltage characteristic could be measured bycontrolling the positive input to amplifier 2292 with a digital toanalog converter (DAC). If each LED 1851 had a dedicated IV sense block1962, no multiplexer 2294 would be needed. Additionally, Voc could bemeasured by adjusting the voltage on the positive terminal of amplifier2292 until no current flows through resistor 2293. Further, switchedcapacitor and sample and hold techniques could be implemented whichwould have a completely different architecture.

FIG. 23 is an example block diagram of display 1411 implemented with aliquid crystal display (LCD) and an LED backlight, which comprises LCDarray 2300, LED array 2301, graphics and timing control circuitry 2302,row driver 2303, column driver 2304, and backlight driver network 2305.

In this example, LCD array 2300 has R rows and C columns of elementswith row driver 2303 producing R number of WR signals and column driver2304 producing C number of DATA signals. Graphics and timing controlcircuitry 2302 provide data and timing to both row driver 2303 andcolumn driver 2304 in a similar manner to an OLED display as describedin FIG. 15.

In this example, LED array 2301 comprises M rows and N columns of LEDsdriven by backlight driver network 2305, which comprises a number of LEDdriver ICs connected together as in the LED display illustrated in FIG.18. LCD array 2300 comprises pixel elements that control the amount oflight that can pass through. LED array 2301 produces the light that isselectively passed through LCD array 2300. When photo-sensitivityparameters, such as Voc and Isc of LEDs 1851 in LED array 2301 aremeasured, row driver 2303 and column driver 2304 configure LCD array2300 to be transparent.

FIG. 23 is just one of many possible block diagrams for display 1411based on LCD and LED backlighting technology. For instance, all LEDelements in LED array 2301 could be directly connected to graphics andtiming control circuitry 2302 through a multiplexer instead of backlightdriver network 2305.

FIG. 24 is an example circuit diagram for the LCD pixel element in LCDarray 2300 and the associated row driver 2303 and column driver 2304,which comprises transistor 2410, capacitor 2411, liquid crystal 2412,buffer amplifier 2413, and inverter 2414. Such pixel element is repeatedhorizontally C times and vertically R times to produce LCD array 2300,with each row of pixel elements controlled by a WR signal from aninverter 2414 in row driver 2303 and each column of pixel elementsconnected to a single DATA signal from buffer amplifier 2413 in columndriver 2304.

The transparency of liquid crystal 2412 is controlled by the voltageacross capacitor 2411, which is set by driving DATA(j) with the desiredvoltage and then pulsing WR(i) high to make transistor 2410 conductive.When WR(i) is high, capacitor 2411 is charged to the voltage on DATA(J),which is driven by buffer amplifier 2413. When photo-sensitivityparameters, such as Voc and Isc of LEDs 1851 in LED array 2301 aremeasured, liquid crystal 2412 for every pixel element in LCD array 2300is made transparent by preferentially setting all WR signals highsimultaneously and setting the voltage on all DATA signals to the valuethat makes liquid crystal 2412 transparent.

FIG. 24 is just one of many possible LCD array 2300, row driver 2303,and column driver 2304 circuit diagrams. For instance, some pixelelements contain multiple transistors to compensate for transistor 2410variations and speed up the write process.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Third Embodiment

LED calibration systems and related methods are also disclosed that usethe photo-sensitivity of LEDs to correct for variations between LEDsduring initial production and over the lifetime of systems using LEDs.Various embodiments are described with respect to the drawings below.Other features and variations can also be implemented, if desired, andrelated systems and methods can be utilized, as well.

In part, the disclosed embodiments relate to using the photo-sensitivityof an LED to determine emission parameters such as intensity andwavelength. Applications for the disclosed embodiments include solidstate lamps, LCD backlights, and LED displays for instance. Variationsin LED brightness and wavelength should be compensated for in order forsuch devices to have uniform color and brightness. Such compensation,which is typically done by measuring the optical output of eachindividual LED with a camera or purchasing specially tested LEDs, isperformed by simply measuring the signal induced on each LED by lightfrom other LEDs in the device or from an additional light source.

The disclosed embodiments include methods to set the color or colortemperature produced by a group of LEDs during the manufacturing of adevice such as a lamp, an LED display, or an LCD backlight, andmaintaining such color or color temperature over the operating life ofsuch a device. The methods involve measuring the intensity andwavelength of light produced by each LED within a group of LEDs andadjusting the amount of light generated by each LED to produce precisecolor and intensity from the group of LEDs.

Two methods that operate some of the LEDs in photovoltaic orphotoconductive mode to measure the light intensity produced by otherLEDs in the group are presented. The first method that uses anadditional light source as a reference determines the light intensityemitted from each LED relative to such reference, while the secondmethod determines the light intensity emitted from each LED relative toeach other. As such, the first method can produce a precise color andintensity from each group of LEDs, while the second method can onlyproduce a precise color.

Both intensity measurement methods typically comprise two steps and canbe used to calibrate devices during both manufacturing and overlifetime. The first step of the first method illustrated in FIGS. 25A-Dand the first step of the second method illustrated in FIG. 27A-D can beperformed in a manufacturing environment on a special control devicethat has all LEDs manually adjusted to produce the desired lightintensities. The results of the first step on such control device arethen used in the second step of the first method illustrated in FIGS.26A-D and the second step of the second method illustrated in FIGS.28A-D on production devices to determine the actual emitted lightintensities.

Both intensity measurement methods can also be used to maintain aprecise color produced by a group of LEDs and uniform intensity from anarray of groups of LEDs, for instance pixels in an LED display, LCDbacklight, or LED lamp, over time. The first step of both methods istypically performed on a device after such device has been calibratedduring manufacturing and the second step is performed in the field atperiodic intervals. The reference light source for the first intensitymeasurement method can be ambient light.

Emission intensity is measured in all cases by measuring thephotocurrent produced in the longest wavelength LED within the group ofLEDs by light from the other LEDs and in the first method from anadditional reference light source. For instance, in an LED array for anLED display or backlight, according to the example shown for the firstmethod, the red LED in a pixel measures the light from the blue andgreen LEDs in the same pixel, and from the reference light source. Next,the red LED in an adjacent pixel measures the light from the first redLED and the reference light source. Such measured light can be reflectedoff a mirror for an LED display during manufacturing or off thewaveguide or diffuser in an LED backlight for instance. In the field,such light can be scattered by the LED packages or enclosures or by anyother means.

In the example shown for the second method, which includes two red LEDsand one white LED in an LED lamp for instance, a first red LED measuresthe light from a second red LED and from the white LED. Next, light fromthe second LED measures the light from the first LED and from the whiteLED. Both the first and second intensity measurement methods can be usedfor any groups of LEDs in any types of products with the differencebetween the methods being the presence or absence of a reference lightsource. The second method could be used in an LED display or backlightto produce precise color and uniform intensity from all pixels by daisychaining the measurements sequentially across such LED array.

The example intensity measurement methods are divided into two stepswhich measure the differences in relative intensity between a known goodmeasurement and the unknown measurement. For instance, duringmanufacturing, a control device with the desired output intensities ismeasured to determine what the relative photocurrents should be. Usingthe first method, the ratios of the photocurrent in a first LED producedby the light from the other LEDs over the photocurrent produced by thereference light source generate coefficients used for the second step.Provided the ratio of intensities from the reference light source in thefirst and second steps is known, the unknown LED intensities in thesecond step can be determined. Likewise, using the second method, theratios of photocurrents induced on one LED by the two other LEDs in acalibrated control device generate coefficients used in the second step.In the second step, the difference in the ratios from the first stepdetermines the difference in relative unknown intensities between thetwo LEDs.

When the first or second method is used to calibrate a device over time,the first step determines what ratios of photocurrents should be andover time the second step determines what they are. The change in suchratios determines the change in actual emission intensity. Since onlyratios currents measured at one time are compared to ratios of currentsat another time, any changes in operating conditions cancel out. Forinstance, such measurements are independent of temperature differences.

The method presented to measure emission wavelength illuminates each LEDwith two different wavelengths of lights, such as a light wavelengthslightly above and below the anticipated peak emission wavelength range,and measures the resulting photocurrent. Since the responsivity of anLED drops off dramatically for incident wavelengths longer than the peakemission wavelength, the difference in induced photocurrents is directlyrelated to the peak emission wavelength. FIGS. 31A-C provide a graphicalillustration of LED responsivity as a function of incident wavelengthand the resulting photocurrent differences.

Since LED emission wavelength does not vary significantly over time,such wavelength measurements can just be performed on a production line.As in the two emission intensity methods, such wavelength measurementshould first be done on a control device with known emission intensityto calibrate the production test setup. Subsequent measurements ofdevices with unknown emission wavelengths, will be relative to thecontrol device results.

Once the emission wavelengths and the emission intensity or relativeemission intensity between a group of LEDs is known, color correctioncoefficients can be determined that adjust the emission intensity oflight from each LED within a group of LEDs to produce a precise colorand optionally a precise intensity from such group of LEDs. FIG. 29illustrates hardware to implement the calibration methods. FIG. 30illustrates color correction coefficients and hardware to correct foremission intensity variations, while FIG. 32 illustrates suchcoefficients and hardware to correct for both emission intensity andwavelength variations between the red, green, and blue LEDs associatedwith a pixel in an LED display or a triplet in an LCD backlight.

Although such calibration methods are appropriate for any devices thatcontain groups of LEDs, of particular interest are LCDs that use FieldSequential Color (FSC). FIG. 33 illustrates a simplified block diagramof a conventional LCD, while FIG. 34 illustrates such a diagram for aFSC LCD. While a conventional LCD has white backlight that is filteredinto red, green, and blue components by special color filters, a FSC LCDeliminates the costly color filters and sequences each color componentat three times the conventional frame rate or more. Such FSC LCDsrequire red, green, and blue backlights and as such are a primaryapplication for the color calibration methods described herein.

The improved methods herein address problems associated with devicesusing groups of different colored LEDs directly or as backlights forillumination. Such calibration methods reduce the need for speciallybinned LEDs for the production of lamps, displays, or backlights, andmaintain the color or color temperature of the light produced over theoperating life of the device.

As stated above, this third embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to this embodiment can beused within the other described embodiments, as desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to calibration and detection systems and methodsdescribed in this third embodiment, as desired. Further, as statedabove, the structures, techniques, systems and methods described withrespect to this third embodiment can be used in the other embodimentsdescribed herein, and can be used in any desired lighting relatedapplication, including liquid crystal displays (LCDs), LCD backlights,digital billboards, organic LED displays, AMOLED (Active Matrix OLED)displays, LED lamps, lighting systems, lights within conventional socketconnections, projection systems, portable projectors and/or otherdisplay, light or lighting related applications.

Turning now to the drawings, FIGS. 25A-D in association with FIGS. 26A-Dillustrate one possible method for calibrating the intensity of lightproduced by each LED within a group of LEDs to produce a specificblended color. Such group of LEDs could be any combination of colors,but as an example comprise red, green, and blue LEDs. Specifically, insuch example, LEDs 2510, 2520, and 2530 could comprise the red, green,and blue light sources respectively in an LED display pixel or LCDbacklight triplet. LED 2540 comprises the red light source in anadjacent LED display pixel or backlight triplet.

FIGS. 25A-D illustrate the first step in such calibration method, whichcan be performed on one special device comprising such group of LEDsthat is representative of many such devices produced on a manufacturingline for instance. Alternatively, such first step could be performed ona device that is to be re-calibrated some time later using the secondstep in such calibration method illustrated in FIGS. 26A-D.

The following equations are associated with FIGS. 25A-D. In particular,equations 1 and 2 are associated with FIG. 25A. Equations 3A and 3B areassociated with FIG. 25B. Equations 4A and 4B are associated with FIG.25C. And equations 5A and 5B are associated with FIG. 25D.

V_(r0n)=E₀R_(r0)  [EQ. 1]

V_(r1n)=E₀R_(r1)  [EQ. 2]

V _(r0gn) =E _(gd) R _(r0) C _(r0g) =E _(gd)(V _(r0n) /E ₀)C_(r0g)  [EQ.3A]

C _(r0g)=(V _(r0gn) /V _(r0n))(E ₀ /E _(gd))  [EQ. 3B]

V _(r0bn) =E _(bd) R ₀ C _(r0b) =E _(bd)(V _(r0n) /E ₀)C _(r0b)  [EQ.4A]

C _(r0b)=(V _(r0bn) /V _(r0n))(E ₀ /E _(bd))  [EQ. 4B]

V _(r1r0n) =E _(r0d) R _(r1) C _(r1r0) =E _(rOd)(V _(r1n) /E₀)C_(r1r0)  [EQ. 5A]

C _(r1r0)=(V _(r1r0n) /V _(r1n))(E ₀ /E _(rOd))  [EQ. 5B]

The light emitted from LEDs 2510 (red), 2520 (green), and 2530 (blue) isadjusted by varying current sources 2511, 2521, and 2531 to produce thedesired light intensities E_(gd), E_(bd), and E_(r0d) from the green,blue, and red LEDs 2520, 2530, and 2510 respectively as shown in FIGS.25B-D. Light source 2550 is adjusted to produce a fixed intensity E₀,which illuminates LEDs 2510 and 2540, induces photo-currentsproportional to incident light intensity, and produces the nominalvoltages V_(r0n) and V_(r1n) across resistors 2512 and 2542 respectivelyas shown in FIG. 25A. Likewise, LEDs 2520 and 2530 illuminate LED 2510as shown in FIGS. 25B-C and LED 2510 illuminates LED 2540 as shown inFIG. 25D to produce the nominal voltages V_(r0gn), V_(r0bn), andV_(r1r0n) respectively across resistors 2512 and 2542. Preferably, theresistance of resistors 2512 and 2542 should be small enough such thatthe induced voltages do not significantly forward bias LEDs 2510 and2540.

The responsivities R_(r0) and R_(r1) of LEDs 2510 and 2540 to incidentlight from light source 2550 as shown in equations 1 and 2 respectivelyare equal to the ratios of the induced voltages V_(r0n) and V_(r1n) overthe incident light intensity E0. As shown in equations 3A-B, the voltageV_(r0gn) induced across resistor 2512 by light from LED 2520 is equal tothe light intensity E_(gd) times such responsivity R_(r0) times acorrection coefficient C_(r0g). Likewise, as shown in equations 4A-B,the voltage V_(r0bn) induced across resistor 2512 by light from LED 2530is equal to the light intensity E_(bd) times such responsivity R_(r0)times the correction factor C_(r0b). Such correction factors C_(r0g) andC_(r0b) take into account differences in emitted light wavelength andoptical attenuation between light from light source 2550, LED 2520, andLED 2530 and incident on LED 2510. For instance, light source 2550 couldproduce red light while LED 2520 and 2530 produce green and bluerespectively. Additionally, light source 2550 could shine directly onLED 2510 while light from LEDs 2520 and 2530 could be indirect sincesuch LEDs could be mounted adjacent to each other. Alternatively, lightfrom LEDs 2510, 2520, and 2530 could be reflected by a mirror in thecase of an LED display or by a light diffusion film in the case of anLCD backlight. As shown in equation 3B, when equation 3A is combinedwith equation 1, such correction coefficient C_(r0g) is equal to theratio of the measured voltages V_(r0gn) over V_(r0gn) times the ratio ofthe known light intensities B₀ over E_(gd). Likewise, when equation 1 issubstituted into equation 4A, C_(r0b) is expressed as a function ofmeasured voltages and known light intensities as shown in equation 4B.

As in equations 3A-B and 4A-B, equations 5A-B relate the nominal voltageV_(r1r0n) induced across resistor 2542 by light from LED 2510 with thedesired intensity E_(r0d). Substituting equation 2 into equation 5Aresults in the correction factor C_(r1r0) being expressed as a functionof measured voltages and known light intensities as shown in equation5B.

With known values for such correction coefficients from a device, suchas an LED display or LCD backlight, with emitted intensities adjusted tothe desired values, the color point of such devices can be adjusted to afixed point on a manufacturing line and maintained in the fieldfollowing the second step in the calibration process illustrated inFIGS. 26A-D. The procedure illustrated in FIGS. 26A-D is performed on adifferent device with LEDs 2510, 2520, and 2530 emitting unknownintensities E_(r0), E_(g), and E_(b) respectively and light source 2550emitting either the same or known intensity on a manufacturing line forinstance or an unknown intensity in the field from ambient light forinstance.

The following equations are associated with FIGS. 26A-D. In particular,equations 6 and 7 are associated with FIG. 26A. Equations 8A, 8B and 8Care associated with FIG. 26B. Equations 9A, 9B and 9C are associatedwith FIG. 26C. And equations 10A, 10B and 10C are associated with FIG.26D.

V_(r0)=E₁R₀  [EQ. 6]

V_(r1)=E₁R_(r1)  [EQ. 7]

V _(r0g) =E _(g) R _(r0) C _(r0g) =E _(g)(V _(r0) /E ₁)C _(r0g)  [EQ.8A]

V _(r0g) =E _(g)(V _(r0) /E ₁)(V _(r0gn) /V _(r0n))(E ₀ /E _(gd))  [EQ.8B]

E _(g) /E _(gd)=(V _(r0g) /V _(r0))(V _(r0n) /V _(r0gn))(E ₁ /E ₀)  [EQ.8C]

V _(r0b) =E _(b) R _(r0) C _(r0b) =E _(b)(V _(r0) /E ₁)C _(r0b)  [EQ.9A]

V _(r0b) =E _(b)(V _(r0) /E ₁)(V _(r0gbn) /V _(r0n))(E ₀ E _(bd))  [EQ.9B]

E _(b) /E _(bd)=(V _(r0b) /V _(r0))(V _(r0n) V _(r0bn))(E ₁ /E ₀)  [EQ.9C]

V _(r1r0) =E _(r0) R _(r1) C _(r1r0) =E _(r0)(V _(r1) /E ₁)C_(r1r0)  [EQ. 10A]

V _(r1r0) =E _(r0)(V _(r1) /E ₁)(V _(r1r0) /V _(r1n))(E ₀ /E_(r0d))  [EQ. 10B]

E _(r0) /E _(r0d)=(V _(r1r0) /V _(r1))(V _(r1n) /V _(r1r0n))(E ₁ /E₀)  [EQ. 10C]

Equations 6 and 7 relate the responsivities R_(r0) and R_(r1) of LEDs2510 and 2540 respectively to the intensity E1 emitted by light source2550. Equation 8A shows the voltage V_(r0g) induced across resistor 2512by the unknown light intensity E_(g) from LED 2520 being equal to E_(g)times R_(r0) times the correction coefficient C_(r0g). Substitutingequation 6 into equation 8A and replacing C_(r0g) with equation 3results in the ratio of the actual emitted intensity E_(g) over thedesired emitted intensity E_(gd) equal to the ratio of the measuredvoltages V_(r0g) over V_(r0) times the ratio of the nominal voltagesV_(r0n) over V_(r0gn) measured as illustrated in FIGS. 25A-D times theratio of intensities E₁ over E₀ emitted by light source 2550, as shownin equations 8B an 8C. Likewise, equations 9A-C and 10A-C express theratios of the unknown intensities E_(b) and E_(r0) over the desiredintensities E_(bd) and E_(r0d) respectively as a function of measuredvoltages and known light intensities emitted from light source 2550.

Since the light intensity produced by an LED changes over time, a devicesuch as an LED display or an LCD backlight with red, green, and blueLEDs, should be re-calibrated after some time to maintain the precisecolor calibrated during production of such device. In such a fieldre-calibration light source 2550 may be daylight or office ambient lightof unknown intensity. In such cases, the ratio E1 over E0 is unknown butis the same for equations 8A-C, 9A-C, and 10A-C so the relativeintensity of light produced by LEDs 2510, 2520, and 2530, andconsequently the color can be maintained. Likewise, the intensity oflight produced by all such pixels or backlight triplets can be keptuniform since the ratio of E1 over E0 should be the same for all suchpixels or triplets.

FIGS. 27A-D in association with FIGS. 28A-D illustrate a method ofcalibrating the light produced by a group of LEDs 2510, 2520, and 2540to produce a fixed color similar to such method illustrated in FIGS.25A-D and 26A-D but without the reference light source 2550. In themethod illustrated in FIGS. 27A-D and 28A-D the relative intensity oflight produced by each LED can be controlled but not the absoluteintensity of the group of LEDs 2510, 2520, and 2540. In this example,LEDs 2510 and 2540 are shown to be red, while LED 2520 is shown to be awhite LED. An example application for such a group of LEDs is a lampemitting white light with a low color temperature similar to that of anincandescent light bulb.

The following equations are associated with FIGS. 27A-D. In particular,equations 11, 12, 13A and 13B are associated with FIGS. 27A-B. Andequations 14, 15, 16A and 16B are associated with FIGS. 27C-D.

V_(r0wn)=E_(wd)R_(r0)C_(rOw)  [EQ. 11]

V_(r0r1n)=E_(r1d)R_(r0)C_(rOr1)  [EQ. 12]

V _(r0wn) /V _(r0r1n)=(E _(wd) /E _(r1d))(C _(r0w) /C _(r0r1))  [EQ.13A]

C _(r0w) /C _(r0r1)=(V _(r0wn) /V _(r0d1n))(E _(r1d) /E _(wd))  [EQ.13B]

V_(r1wn)=E_(wd)R_(r1)C_(r1w)  [EQ. 14]

V_(r1r0n)=E_(rOd)R_(r1)C_(r1r0)  [EQ. 15]

V _(r1wn) V _(r1r0n)=(E _(wd) /E _(r0d))(C _(r1w) /C _(r1r0))  [EQ. 16A]

C _(r1w) /C _(r1r0)=(V _(r1wn) /V _(r1r0n))(E _(r0d) /E _(wd))  [EQ.16B]

The following equations are associated with FIGS. 28A-D. In particular,equations 17, 18, 19A and 19B are associated with FIGS. 28A-B. Andequations 20, 21, 22A, 22B and 23 are associated with FIGS. 28C-D.

V_(r0w)=E_(w)R_(r0)C_(r0w)  [EQ. 17]

V_(r0r1)=E_(r1)R_(r0)C_(r0r1)  [EQ. 18]

V _(r0r1) N _(r0w)=(E _(r1) /E _(w))(C _(r0r1) /C _(r0w))  [EQ. 19A]

E _(r1) E _(w)=(V _(r0r1) /V _(r0w))(C _(r0w) /C _(r0r1))=(V _(r0r1) N_(r0w))(V _(r0wn) N _(r0r1n))(E _(r1d) E _(wd))  [EQ. 19B]

V_(r1w)=E_(w)R_(r1)C_(r1w)  [EQ. 20]

V_(r1r0)=E_(r0)R_(r1)C_(r1r0)  [EQ. 21]

V _(r1r0) /V _(r1w)=(E _(r0) /E _(w))(C _(r1r0) /C _(r1w))  [EQ. 22A]

E _(r0) /E _(w)=(V _(r1r0) /V _(r1w))(C _(r1w) /C _(r1r0))=(V _(r1r0) /V_(r1w))(V _(r1wn) /V _(r1r0n))(E _(r0d) /E _(wd))  [EQ. 22B]

E _(r0) /E _(r1)=(E _(r0) /E _(w))/(E _(r1) /E _(w))[EQ. 23]

The first step in such calibration method as shown in FIGS. 27A-D is toadjust current sources 2511, 2521, and 2541 to produce the desired lightintensities E_(r0d), E_(wd), and E_(r1d) from LEDs 2510, 2520, and 2540respectively as shown in FIGS. 27A-D. Then the light from LED 2520 andLED 2540 are measured by LED 2510, which produce the nominal voltagesV_(r0wn) and V_(r0r1n) respectively across resistor 2512 as shown inFIGS. 27A and 27B. Equations 11 and 12 illustrate the relationshipbetween such voltages, emitted powers, responsivity, and correctionfactors. Equations 13A-B take the ratio of equation 11 over 12 toproduce the ratio of correction coefficients C_(r0w) over C_(r0r1)expressed as a function of the ratio of nominal voltages V_(r0wn) overV_(r0r1n) times the ratio of desired emission intensities E_(r1d) overE_(wd).

Next the light from LEDs 2520 and 2510 are measured by LED 2540, whichproduce the nominal voltages V_(r1wn) and V_(r1r0n) respectively acrossresistor 2542 as shown in FIGS. 27C and 27D. Equations 14 and 15 relatesuch voltages to emitted powers, responsivity, and correction factors.Equations 16A-B take the ratio of equation 14 over 15 to produce theratio of correction coefficients C_(r1w) over C_(r1r0). Once such ratiosof correction coefficients are known, the relative intensities of lightproduced by similar such devices on a manufacturing line can bedetermined and adjusted to produce a desired color. Likewise, suchdevices can be re-calibrated in the field after use to maintain thedesired color.

FIGS. 28A-D illustrate the second step in the method to calibrate colorwithout a reference light source. In such second step, LEDs 2520 and2540 sequentially illuminate LED 2510 with unknown light intensitiesE_(v), and E_(d) respectively, which produce voltages V_(r0w), andV_(r0r1) respectively across resistor 2512 as shown in FIGS. 28A and28B. Equations 17 and 18 relate the induced voltages V_(r0w) andV_(r0r1) to the emitted powers E_(w) and E_(r1), the responsivityR_(r0), and the correction coefficients C_(r0w) and C_(r0r1)respectively. Equations 19A-B take the ratio of equation 18 over 17 andsubstitutes equation 13B for the ratio of correction coefficientsC_(r0w) over C_(r0r1) to express the ratio of emitted intensities E_(r1)over E_(w) as a function of measured voltages and desired emittedintensities.

Next, LEDs 2520 and 2510 sequentially illuminate LED 2540 with unknownlight intensities E_(w) and E_(r0) respectively, which produce voltagesV_(r1w) and V_(r1r0) respectively across resistor 2542 as shown in FIGS.28A-D. Equations 20 and 21 relate the induced voltages V_(r1w) andV_(r1r0) to the emitted powers E_(w) and E_(r0), the responsivity Rd,and the correction coefficients C_(r1w) and C_(r1r0) respectively.Equations 22A-B take the ratio of equation 21 over 20 and substitutesequation 16B for the ratio of correction coefficients C_(r1w) overC_(r1r0) to express the ratio of emitted intensities E_(r0) over E_(w)as a function of measured voltages and desired emitted intensities.Equation 23 expresses the ratio of E_(r0) over E_(r1) as the ratio ofequation 22B over equation 19B. Once such relative intensities emittedfrom each LED 2510, 2520, and 2540 are known, such intensities can beadjusted to produce the desired color.

FIGS. 25A-D, 26A-D, 27A-D and 28A-D illustrate just two of many possiblemethods for calibrating the color point emitted from a group ofdifferent colored LEDs using such LEDs as photo-detectors. Any number ofLEDs in some cases from two to many more can be calibrated using suchmethods or other methods. Any color LEDs can be used provided the LEDsused as photo-detectors measure the light produced by LEDs with roughlyequal or shorter wavelengths. Although FIGS. 25A-D and 26A-D use red,green, and blue LEDs common in LED panels and increasingly in LEDbacklights, such method is equally appropriate for a lamp or any othertype of illumination or display device including Organic LEDs (OLEDs).Although FIGS. 27A-D and 28A-D use white and red LEDs in a lamp as anexample, such calibration method is equally appropriate for an LEDdisplay, backlight, or any other type of illumination device includingOLEDs. Such methods could be performed on a manufacturing line to ensureconsistent color of devices or could be performed on the same deviceover time to maintain color.

FIG. 29 is an example block diagram for circuitry that can implement themethods illustrated in FIGS. 25A-D, 26A-D, 27A-D and 28A-D whichcomprises integrated circuit (IC) 2980, LEDs 2510, 2520, 2540, andoptionally 2530, and resistors 2512 and 2542. Integrated circuit (IC)2980 further comprises timing and control circuitry 2981, coefficientmatrix 2982, digital to analog converter (DAC) 2983, analog to digitalconverter (ADC) 2984, and three or four output drivers 2985 forproducing currents for LEDs 2510, 2520, 2530 (optional) and 2540,depending upon whether optional LED 2530 is included. Output drivers2985 further comprise of pulse width modulators 2987 and current sources2986.

Timing and control circuitry 2981 manages the functionality of driver IC2980. Illumination data for LEDs 2510, 2520, 2530, and 2540 is eitherhardwired into timing and control circuitry 2981 or is communicated totiming and control circuitry 2981 through some means, and is forwardedat the appropriate time to the color correction matrix 2982. Colorcorrection matrix 2982 can, among other things, adjust the illuminationdata for LEDs 2510, 2520, 2530, and 2540 to compensate for variationsbetween LEDs to produce uniform brightness and color across a display orfrom a lamp. Matrix 2982 can comprise correction coefficients that whencombined with the illumination data produce the data forwarded to outputdrivers 2985, which have pulse width modulators 2987 that produce logiclevel signals that turn current sources 2986 on and off to LEDs 2510,2520, 2530, and 2540.

ADC 2984 has access to both terminals of LEDs 2510 and 2540 and can,among other things, measure the voltage produced across resistors 2512and 2542 in response to light incident on LEDs 2510 and 2540. The anodesof all three or four LEDs in this example, depending upon whetheroptional LED 2530 is used, can be tied together to a single supplyvoltage Vd 2988, or can be connected to different supply voltages. Inthe case all LEDs 2510, 2520, 2530 (optional), and 2540 are of onecolor, all anodes preferentially would be connected together. In thecase such LEDs 2510, 2520, 2530 (optional), and 2540 are of differentcolors, each such different color LED 2510, 2520, 2530 (optional), and2540 would preferentially be connected to each such different supplyvoltage.

FIG. 29 is just one example of many possible driver IC 2980 blockdiagrams. For instance PWM 2987 would not be needed if LEDs 2510, 2520,2530, and 2540 were driven with variable current for fixed amount oftimes. Resistors 2512 and 2542 would not be needed if ADC 2984 measuredopen circuit voltage, short circuit current, or some other combinationof current and voltage from LEDs 2510 and 2540. DAC 2983 could be afixed current source if variable currents were not desired. Colorcorrection matrix 2982 could reside elsewhere in a device.

FIG. 30 is an example block diagram of correction matrix 2982 that cancorrect for variations in light intensity produced by a combination ofred, green, and blue LEDs 2510, 2520, and 2530 to produce relativelyuniform brightness and color across a display for from a lamp. Matrix 82comprises memory 3090 that can store correction coefficients C_(r),C_(g), and C_(b), which are combined by multipliers 3091 with the red,green, and blue, for instance, illumination data respectively fromtiming and control circuitry 2981 to produce the illumination dataforwarded to modulators 2987 controlling red, green, and blue LEDs 2510,2520, and 2530 respectively. Such correction coefficients are typicallyrelatively large, which produce adjustments in the illumination data tocompensate for variations between LEDs 2510, 2520, and 2530.

Memory 3090 can be made from SRAM, DRAM, FLASH, registers, or any otherform of read-writable semiconductor memory. Such correction coefficientsperiodically can be modified by driver IC 2980 or any other processingelement in a display or lamp for instance to adjust for changes in LEDs2510, 2520, and 2530 characteristics for instance over temperature orlifetime.

Multipliers 3091 scale the illumination data from timing and controlcircuitry 2981 by multiplying each color component by the correspondingcorrection coefficient. Such multiplication can be performed by discreethardware in bit parallel or bit serial form, in an embeddedmicrocontroller, or by any other means. Preferentially, one hardwaremultiplier comprising a shifter and an adder performs all threemultiplications. As such, FIG. 30 is just one of many possible blockdiagrams for correction matrix 2982. Likewise, correction matrix 2982could reside elsewhere in a device, such as software in a graphicscontroller.

FIGS. 31A-C illustrate one possible method to determine the peakemission wavelength λ_(p) from an LED by determining such LED'sphotosensitivity as a function of the wavelength of light incident onsuch LED. Such measurement system could comprise light source 2550, LED2510 and resistor 2512 as illustrated in FIGS. 25A-D, with thewavelength of light emitted by light source 2550 switched betweenwavelengths λ⁻ and λ₊ that are slightly shorter and longer respectivelythan the expected peak emission wavelength λ_(p) of LED 2510.

Plot 3100 in FIG. 31A represents the photosensitivity of LED 2510 with anominal peak emission wavelength λ_(pn) as a function of incidentwavelength with the vertical axis representing the voltage inducedacross resistor 2512. At wavelengths longer than λ_(pn), thephotosensitivity reduces significantly, while at wavelengths shorterthan λ_(pn), the photosensitivity reduces linearly with wavelength. Alsoshown is incident light with wavelength λ⁻ producing voltage V⁻ acrossresistor 2512 and incident light with wavelength λ₊ producing voltage V⁻across resistor 2512. Line 3103 connecting the points (λ⁻, V⁻) and(λ₊,V⁻) has a slope M=(V−−V+)/(λ⁻λ₊).

Plot 3101 in FIG. 31B illustrates the photosensitivity of an LED 2510with a peak emission wavelength λ_(p−) that is slightly shorter than thenominal peak emission wavelength λ_(pn). When such an LED 2510 isilluminated by light source 2550 with wavelengths λ⁻ and λ₊, voltages V⁻and V₊ respectively are generated across resistor 2512. The differencein voltage between such V⁻ and V₊ is greater for such LED 2510 with peakemission wavelength λ_(p−) that is slightly shorter than the nominalpeak emission wavelength λ_(pn) than for such LED 2510 with the nominalpeak emission wavelength λ_(pn). Additionally, the slope M of line 3104is more negative for the LED 2510 emitting the peak wavelength λ⁻, thanfor the LED 2510 emitting the nominal peak wavelength λ_(pn).

Plot 3102 in FIG. 31C illustrates the photosensitivity of an LED 2510with a peak emission wavelength λ_(p+) that is slightly longer than thenominal peak emission wavelength λ_(pn). When such an LED 2510 isilluminated by light source 2550 with wavelengths λ⁻ and λ₊ voltages V⁻and V₊ respectively are generated across resistor 2512. The differencein voltage between such V⁻ and V₊ is smaller for such LED 2510 with peakemission wavelength λ₊ that is slightly longer than the nominal peakemission wavelength λ_(pn) than for such LED 2510 with the nominal peakemission wavelength λ_(pn). Additionally, the slope M of line 3105 isless negative for the LED 2510 emitting the peak wavelength λ₊, than forthe LED 2510 emitting the nominal peak wavelength λ_(pn).

Since the slopes of lines 3103, 3104, and 3105 in FIGS. 31A, 31B and 31Care directly related to the peak emission wavelength of LED 2510, suchslopes can be used to determine such peak emission wavelengths. Forinstance, such relationship could be linear. FIGS. 31A-C illustrate oneof many possible methods to determine the peak emission wavelength oflight produced by an LED by measuring the photosensitivity of such LED.For instance, LED light induced current could be measured instead ofvoltage or some other combination of current and voltage could bemeasured. Additionally, light with broader spectrums of light couldinduce such voltages or currents instead of the mono-chromatic sourcesillustrated in FIGS. 31A-C.

FIG. 32 is an example block diagram for correction matrix 2982 that cancorrect for variations in both light intensity and wavelength producedby a combination of red, green, and blue LEDs 2510, 2520, and 2530 forinstance to produce uniform brightness and color from an array of LEDs.Matrix 2982 comprises memory 3090 that can store nine correctioncoefficients with three such coefficients for each color componentproduced. Coefficients C₀, C_(gg), and C_(bb) would typically beeffectively the same as C_(r), C_(g), and C_(b) from FIG. 30 to adjustfor intensity variations in LEDs 2510, 2520, and 2530, while theremaining coefficients (Crg, Crb, Cgr, Cgb, Cbr, Cbg) compensate forwavelength variations.

For instance, if the red illumination data from timing and controlcircuitry 2981 was intended for an LED 2510 with a wavelength of 650 nmand the connected LED 2510 wavelength was exactly 650 nm, coefficientsC_(gr) and C_(br) would be zero and C_(π) would be close to one. If suchconnected LED 2510 wavelength was 660 nm and had the same intensity asthe just previous example, C_(π) would be slightly smaller than in thejust previous example and C_(gr) and C_(br) would be non-zero, whichwould produce some light from such green and blue LEDs 2520 and 2530respectively. The combination of light from such red, green, and blueLEDs 2510, 2520, and 2530 would be perceived the same as if the red LED2510 emitted at 650 nm.

Memory 3090 and multipliers 3091 can operate and be implemented asdescribed for FIG. 6. Adder 3210 sums the multiplication results fromthe three connected multipliers 3091 to produce the illumination dataforwarded to modulators 2987. Such adders 3210 can be implemented inhardware or software, or be performed bit parallel or bit serial. FIG.32 is just one of many possible intensity and wavelength correctionmatrix 2982 block diagrams.

FIG. 33 is an example simplified block diagram of an LCD displaycomprising of backlight 3321, diffuser 3322, polarizers 3323 and 3326,color filter 3324, and liquid crystal array 3325. Image pixel 3330 isexpanded to illustrate liquid crystal sub-pixel elements 3331, whichmodulate the amount of red, green, and blue light from color filterpixel element 3332, to produce a particular color and intensity fromsuch image pixel 3330. The backlight 3321 produces white light from oneor many light sources, such as LED 3333, that is made uniform across thedisplay by diffuser 3322. Polarizer 3323 only lets a particularpolarization of light through to color filter 3324, which produces red,green, and blue light. Liquid crystal array 3325 selectively rotates thepolarization of such light, which is then filtered by polarizer 3326 toproduce a color image of pixels 3330. Backlight 3321 typically comprisesone or more white LEDs 3333, but could comprise a color calibratedcombination of red, green, and blue LEDs.

FIG. 34 is an example simplified block diagram of LCD 3440 thateliminates color filter 3324 by sequencing the red, green, and bluecolors through a single liquid crystal pixel element 3331 three times asfast as LCD 3320. Such a display is commonly called a Field SequentialColor (FSC) LCD, which costs significantly less than and consumes muchless power than LCD 3320, because the color filter is eliminated. Sincethe red, green, and blue colors are typically sequenced, white LED 3333is replaced by red, green, and blue LEDs 2510, 2520, and 2530. Currentsource 3334 is replaced with driver IC 2980 that sequentially enablesLEDs 2510, 2520, and 2530 by sequentially sinking current through theenable signals enr 3441, eng 3442, and enb 3443 respectively. Toestablish and maintain a precise average color produced by thecombination of light from LEDs 2510, 2520, and 2530, the methodsillustrated in FIGS. 25A-D, 26A-D, 27A-D, 28A-D, and 31A-C can beperformed by driver IC 2980 or other circuitry.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Fourth Embodiment

Illumination devices and related systems and methods are disclosed thatcan be used for LCD (Liquid Crystal Display) backlights, LED lamps, orother applications. The illumination devices can include a photodetector, such as a photodiode or an LED or other light detectingdevice, and one or more LEDs of different colors. A related method canbe implemented using these illumination devices to maintain precisecolor produced by the blended emissions from such LEDs. Other methods,systems and applications for these illumination devices can also beimplemented, as desired. One application for the illumination devices isbacklighting for FSC (Field Sequential Color) LCDs (Liquid CrystalDisplays). FSC LCDs temporally mix the colors in an image bysequentially loading the red, green, and blue pixel data of an image inthe panel and flashing the different colors of an RGB backlight. Preciseand uniform color temperature across such a display can beadvantageously maintained by continually monitoring ratios of photocurrents induced by the different colored LEDs in each illuminationdevice as each color is flashed. Various embodiments are described withrespect to the drawings below. Other features and variations can also beimplemented, if desired, and related systems and methods can beutilized, as well.

As described further below, example embodiments for illumination devicesare disclosed that include LEDs with different emission wavelengths anda photo detector. In addition, a method is disclosed to maintain aprecise color and intensity emitted from the combination of LEDs in theillumination device. The disclosed embodiments, for example, can be usedfor LCDs using FSC in which typically only one color LED from a group ofred, green, and blue LEDs emit light at any one time. Such embodimentscan also be used for conventional LCD backlights and LED lamps in whichall the LEDs typically emit at the same time, but periodically sequencethe colors for measurement. The embodiments can also be used in othersystems and applications, if desired.

In one embodiment, as further described below, a photo detector in aillumination device including red, green, and blue LEDs can be used tomonitor (e.g., continually, periodically, etc.) the intensity of lightproduced by each color LED. A controller, such as a controllerintegrated circuit (IC), for example, can then use the intensitymeasurements to maintain the fixed blended color and intensity producedby the LEDs. One method that can be performed by the controller IC tocontrol color includes comparing ratios of signals induced in the photodetector by the different colored LEDs to desired ratios, for example,as described herein with respect to the third and seventh embodiments.Desired ratios can be determined, for example, during manufacturing ofthe illumination device or the display. It is noted that the photodetector can be any light detecting device including but not limited toa silicon photodiode, a discreet LED, a light detecting LED or a lightdetecting LED integrated on the same die as one of the light emittingLEDs. As such, in the discussions below addressing the use ofphotodiodes, it is understood that other light detectors can be usedinstead of the photodiode, including a discreet LED, a light detectingLED, a light detecting LED integrated on the same die as one of thelight emitting LEDs or some other light detecting device.

Although the intensity control process could be performed continually asin the color control process, preferentially intensity control can alsobe performed periodically in response to a user command or power up.Other control timing could also be applied if desired. Because the humaneye is much more sensitive to variations in color than in intensity,small intensity variations can typically be tolerated by the human eye.

Although one primary application for the invention is backlights for FSCLCDs, many other applications such as solid state lighting andconventional LCDs could also benefit from the disclosed embodiments. Forexample, combining a photo detector, such as a photodiode or an LED orother light detecting device, with different colored LEDs, includingwhite, in the same package enables the light produced by each such LEDto be accurately measured even in the presence of significant ambientlight or light from LEDs in adjacent packages. In one embodiment, aphotodiode enables the temperature of the package and consequently theLEDs to be easily and accurately measured using well known techniquesthat inject currents into such photodiode, measure forward voltages, andcalculate temperature from the results. With such measurements, thecolor and intensity of the light produced by such an illumination devicecan be accurately controlled using the methods described herein for anyapplication. The ratio of photo currents can be used to control therelative intensity and consequently the color of light produced by thedevice and the absolute photo current compensated for temperature can beused to control the total intensity produced by the device.

While the embodiments described herein are applicable to a broad rangeof applications, it is noted, however, that the disclosed embodimentsare particularly useful for FSC LCD backlights, because the colors aresequenced and as such the photo detector (e.g. photodiode, LED, etc.)can monitor the light produced by each LED in the illumination devicewithout requiring modifications to the display timing or optics.

As stated above, this fourth embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to the second, third, seventhand eighth embodiments can be used with respect to the systems andmethods described in this fourth embodiment, as desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to systems and methods described in this fourthembodiment, as desired. Further, as stated above, the structures,techniques, systems and methods described with respect to this fourthembodiment can be used in the other embodiments described herein, andcan be used in any desired lighting related application, includingliquid crystal displays (LCDs), LCD backlights, digital billboards,organic LED displays, AMOLED (Active Matrix OLED) displays, LED lamps,lighting systems, lights within conventional socket connections,projection systems, portable projectors and/or other display, light orlighting related applications.

As described below, in some embodiments, the illumination device caninclude one or more colored LEDs, such as a red LED, a green LED, and ablue LED, and a silicon photodiode or other photo detector (e.g., LED,etc.) packaged together as shown in FIGS. 35 and 40. FIG. 35 illustratesthe preferential illumination device which includes a photo detector,such as a silicon photodiode or other light detecting device, integratedon the controller IC illustrated in FIG. 36 that measures such LEDoutput light and temperature, and performs a method to maintain precisecolor and intensity produced by such LEDs. FIG. 40 illustrates analternative illumination device including a photo detector, such as adiscreet silicon photodiode or other light detecting device, that isused to measure LED output light and illumination device temperature.The external controller IC illustrated in FIG. 41 can be used toimplement a color and intensity control method for any number ofillumination devices. Although the discussions below primarily use asilicon photodiode as the photo detector, it is again noted that thephoto detector can be any light detecting device including but notlimited to a silicon photodiode, a discreet LED, a light detecting LEDor a light detecting LED integrated on the same die as one of the lightemitting LEDs.

FIGS. 37, 38, and 39 illustrate possible photodiode current andtemperature measurement circuitry, simplified system connection diagram,and timing diagram respectively for the preferential illumination devicecomprising the photodiode integrated on the controller IC. Likewise,FIGS. 42, 43, and 44 illustrate the same for the illumination devicecomprising the discreet photodiode. Because an LCD backlight typicallyneeds many illumination devices to provide uniform and sufficientbrightness across the display, the system connection diagrams illustratehow such illumination devices can be connected together and to thecontroller IC in the case of the illumination device comprising adiscreet photodiode.

Because an LCD backlight typically has many illumination devices,packaging the photodiode with each set of red, green, and blue LEDshelps to minimize the affect light from adjacent LEDs has on thephotodiode current induced in a first illumination device by LEDs insuch first illumination device. Further, the illumination device packagecan include an opaque body to block the direct light between adjacentillumination devices and clear plastic fill to allow light to be emitteddirectly into a display waveguide or diffuser. Some light from adjacentillumination devices can scatter from such waveguide or diffuser intosuch first illumination device, but provided the photodiode resides inthe illumination device the amount of such scattered light is typicallysufficiently small to not affect the measurement.

As shown in the example timing diagrams illustrated in FIGS. 39 and 44,only one color of the red, green, and blue LEDs are emitting at one timein the backlight for an FSC LCD, which enables the photodiode in eachillumination device to continually measure the light produced by eachsuch LED. Additionally because scattered light from adjacentillumination devices is sufficiently small, the light produced by allthe LEDs in all the illumination devices in an FSC LCD backlight can bemeasured simultaneously without requiring modifications to the displaytiming and without special waveguides necessary with conventional RGBbacklights. Timing diagrams for other applications, such as conventionalLCD backlighting or LED lamps for general illumination, are not shown,but would preferentially have all LEDs emitting simultaneously most ofthe time. Periodically, each color LED would emit independently formeasurement.

FIGS. 39 and 44 also illustrate two different approaches for driving theLEDs in the illumination devices, which reduce the number of packagepins required when using an integrated photodiode and a discreetphotodiode respectively. As shown in FIG. 36, the power supply for thered LED also provides power for the controller IC. Because the forwardvoltages for green and blue LEDs are typically similar, the power supplyfor both such LEDs is shown to be the same. Additionally, as shown inFIG. 39, such green and blue LED power supply preferentially goes highafter such red LED power supply, which generates a reset pulse on thecontroller IC.

As shown in FIG. 41, the power supplies for the red, green, and blueLEDs are separate, but all three cathodes are connected to one pin onthe controller IC. As shown in FIG. 44, such LED power suppliessequentially turn on with only one being high at one time. As such, oneLED driver on the controller IC can be used to drive all three LEDs inone illumination device.

FIG. 45 illustrates possible circuitry in a controller IC to implementthe LED color and intensity control method for the illumination device,which can include three steps or processes that include factorycalibration, color control, and/or intensity control, if desired.

During factory calibration, which would occur at the time anillumination device or a backlight or display is manufactured, theintensity and wavelength of the red, green, and blue LEDs of eachillumination device can be measured, coefficients to compensate for suchvariations can be generated, and the temperature and the photodiodecurrent induced by each LED when producing the desired amount of lightcan be measured. Such correction coefficients, photodiode currents, andtemperature measurements can then be stored in a correspondingcontroller IC, if such IC has non-volatile memory, and used directly, orthey can be stored in some common memory for all illumination devices ina display and loaded each time such display powers up for instance.

During normal operation, the color produced by the combination of lightfrom the red, green, and blue LEDs can be precisely maintained bycomparing the ratios of photodiode currents induced by the LEDs in anillumination device to the ratio of the desired photodiode currentsmeasured during factory calibration. Because the intensity of lightproduced by the blue LED remains relatively constant over temperature,the color control process can use the photocurrent induced by the blueLED as a reference. The photodiode currents induced by the red and greenLEDs can be divided by the photodiode current induced by the blue LEDsto produce both the actual measured ratios of red over blue and greenover blue and the factory desired ratios of red over blue and green overblue. The differences between the actual ratios and the desired ratioscan then be low pass filtered before adjusting the average drive currentto the red and green LEDs. The color control process can then compareratios of photodiode currents to cancel any measurement variations thatoccur over operating conditions such as temperature and power supplyvoltage and over lifetime. Because the color of light produced by acombination of different colored LEDs is determined by the relativeintensity produced by each such LED, comparing ratios of photodiodecurrents is well suited for the color control process.

To maintain a relatively precise intensity produced by the illuminationdevice, the intensity control process can be configured to compare themeasured photodiode current induced by the blue LED during operation tothe desired photodiode current induced by the blue LED measured duringfactory calibration. Because such measured photodiode current can varywith temperature, the temperature of the photodiode, which should benearly the same as the LEDs in the same package, is also measured andthe measured photodiode current can be compensated appropriately beforebeing compared to the desired photodiode current. The difference betweenthe temperature compensated and the desired photodiode currents can bestored in a register, which adjusts the average blue LED drive currentaccordingly.

Turning now to the drawings, FIG. 35 illustrates an illumination device3510 that comprises an integrated circuit 3511 with a photo detector3512 and three LEDs, one for each of the colors red 3513, green 3514,and blue 3515. The photo detector 3512 can be, for example, a siliconphotodiode, and the discussions below primarily use a photodiode as thephoto detector. However, as indicated above, the photo detector 3512 canalso be any other light detecting device, as desired. The packageencapsulating the IC and LEDs comprises a four pin leadframe 3516, anopaque plastic body 3517, and a clear plastic fill 3518 that allowslight from the LEDs to emit vertically from the package. The leadframe3516 comprises four pins for the signals Vr 3519, Vbg 3520, Din 3521,and Dout 3522. The signal Vr 3519 provides the power to the red LED 3513and the controller IC 3511, the signal Vbg 3520 provides the power tothe green LED 3514 and the blue LED 3515, and the Din 21 and Dout 22signals communicate data and control information into and status fromthe controller IC 11. The backside of the illumination device is acommonly used exposed pad that provides good thermal conduction to aprinted circuit board and an electrical ground connection. It is alsonoted that on an integrated circuit, if desired, the silicon photodiodecan be implemented as a diffused junction between a P-type substrate andan N-type diffusion layer. Further, if desired, the silicon photodiodecan also be implemented as a diffused junction between an N-typesubstrate and a P-type diffusion later.

During calibration for some applications and during normal operation forFSC LCD backlighting applications, the integrated circuit 3511sequentially provides current to the different colored LEDs, whichresults in only one LED producing light at a time. The siliconphotodiode 3512 and associated detection circuitry continually monitorthe light produced by each LED. Control circuitry adjusts the averagecurrent provided to each LED to maintain a precise illuminationintensity and color. The blue LED 3515 and green LED 3514 typically havetwo surface contacts and are shown to be flip chip mounted to theintegrated circuit 3511. The red LED 3513 typically has one surfacecontact and one backside contact and is shown to be attached directly tothe integrated circuit 3511 with the top surface contact wire bonded toVr 3519.

FIG. 35 is one of many possible illumination devices that combine an LEDcontroller IC 3511 with an integrated photo detector, such as a siliconphotodiode or other light detecting device, and a set of differentcolored LEDs in the same package. The example illustrated in FIG. 35shows a combination of red, green, and blue LEDs, but such illuminationdevice could comprise any color LEDs including the combination of whiteand red LEDs for general lighting or conventional LCD backlightingapplications. The illumination device 3510 is also shown to have fourpins and a backside contact for ground, but could have a wide variety ofpin combinations. The LEDs are also shown to be attached directly to theintegrated circuit 3511, but could be attached in a variety of waysincluding being mounted to the leadframe 3516 or to some other form ofsubstrate and wire bonding to the IC 3511. Further, as noted above, thephoto detector depicted as a photodiode can be any light detectingdevice, as desired, including but not limited to a silicon photodiode, adiscreet LED, a light detecting LED or a light detecting LED integratedon the same die as one of the light emitting LEDs.

FIG. 36 illustrates a possible LED controller IC 3511 that provides thedrive current to the red 3513, green 3514, and blue 3515 LEDs andmonitors the light produced by such LEDs and measures the illuminationdevice 3510 temperature using the silicon photodiode 3512 andmeasurement block 3630. Network interface 3634 receives illumination andcontrol data from signal Din 3521 and produces status information onsignal Dout 3522. Such illumination data can adjust the intensity andoptionally the color of light produced by each illumination device 3510to support local dimming. Oscillator 3635 provides a reference clock tonetwork interface 3634, which can recover a clock from the data receivedon Din 3521 that can be used to clock the rest of integrated circuit3511. Timing and control circuitry 3633 uses the recovered clock tomanage the operation and functionality of integrated circuit 3511.

The color adjustment circuitry 3636 performs the tasks necessary tomaintain precise LED illumination intensity and color produced by theLEDs. Such tasks include monitoring the current produced by thephotodiode and adjusting the digital values forwarded to the pulse widthmodulators 3638, 3639, and 3640 that control the amount of time thatcurrent sources 3641, 3642, and 3643 draw current through signals PWMr(red) 3647, PWMg (green) 3648, and PWMb (blue) 3649 that are connectedto LEDs 3513, 3514, and 3515 respectively. Also shown is low dropout(LDO) regulator 3637 producing the power supply VDD 3645 for IC 3511from Vr 3519 and reset circuitry 3644 producing the master reset signal/RST 3646 for IC 3511 from Vbg 3520. Example voltage values for Vr 3519,Vbg 3520, and VDD 3645 could be 2.5 v, 3.5 v, and 1.8 v respectively.

FIG. 36 is one of many possible block diagrams for a controller ICcomprising a photodiode or other light detecting device, such as an LED,and producing the drive current to any number of LEDs. For instance, theillumination intensity produced by such LEDs could be controlled byadjusting the current produced by current sources instead of controllingthe amount of time such current sources are producing current usingpulse width modulators. Additionally, the control and data signals intoand out of the controller IC could be completely different. Forinstance, illumination data and control data could have separate inputpins. Likewise, a clock could be input with data instead of recovering aclock from the data.

FIG. 37 is illustrates a possible block diagram for measurement block3630 contained within control IC 3511. In this example, amplifier 3750is configured as a trans-impedance amplifier that forces the currentproduced by photodiode 3512 through resistor 3751 with amplifier 3750maintaining a relative fixed voltage on the photodiode cathode. Thevoltage developed across resistor 3751 is forwarded to mux 3756 and ADC3757.

The temperature sensor comprises current sources 3752 and 3753 sourcingcurrent I₀ into diodes 3754 and 3755. Diode 3755 comprises ten diodeswith the same physical and electrical characteristics at diode 3754connected in parallel to produce a diode 3755 with ten times the area asdiode 3754. The voltage difference between the anodes of diodes 3754 and3755 is proportional to absolute temperature and is forwarded to ADC3757 through mux 3756.

FIG. 37 is one of many possible block diagrams for measurement block3630. For instance, temperature could be measured by forcing twodifferent currents in the forward biasing direction through photodiode3512 and measuring the differences in the resulting two voltages. Thepolarity of photodiode 3512 could be reversed and an amplifier could beconfigured to force zero volts across photodiode 3512. Additionally,amplifier 3750 could be eliminated and resistor 3751 could be connectedacross photodiode 3512 to produce a voltage proportional to the currentproduced by photodiode 3512. As such, FIG. 37 is just one example ofmany possible block diagrams for photocurrent and temperaturemeasurement.

FIG. 38 illustrates a possible connection diagram for multipleillumination devices with integrated photodiodes in a display backlight.Illumination devices 3510 illustrate a group of any number of instancesof illumination device 3510 that are serially connected together byconnecting the Dout signal 3522 of one illumination device 3510 to theDin signal 3521 of the next serially connected illumination device 3510.The Dout signal 3522 of the last illumination device 3510 is connectedto video controller 3861, which also provides the Din signal 3521 to thefirst illumination device 3510 and completes a communication ringbetween video controller 3861 and all the illumination devices. Videocontroller 3861 can produce the illumination intensity and color datafor each illumination device 3510 and can control and monitor thefunctionality of all such devices.

Power supply 3860 provides the Vr 3519 and Vbg 3520 power supplies tothe red, and the green and blue LEDs respectively for all theillumination devices 3510. Such power supplies can be static or can beswitched as illustrated in FIG. 39. Power supply 3860 is also shown toprovide power to video controller 3861, which typically would be a fixedvoltage.

In a display backlight, illumination devices 3510 can be connectedserially along one or more edges of a liquid crystal panel in a socalled edge lit LCD or in an array behind the liquid crystal panel in aso called direct lit LCD. In edge lit LCDs and in some direct lit LCDs,the illumination devices should provide uniform intensity and colorbehind the liquid crystal panel, with the pixels in the panel producingthe image by letting more or less different colored light through. Somedirect lit LCDs implement local dimming in which the brightness andsometimes color of each illumination device 3510 or groups ofillumination devices can be controlled uniquely for each image frame.

FIG. 38 is one of many possible connection diagrams for illuminationdevices 3510 in a display. For instance, video controller 3861 couldconnect to multiple chains of illumination devices 3510. Additionallyvideo controller 3861 could be a graphics or an I/O controller forinstance. Chains of illumination devices could be any number includingjust one. The Vr 3519 and Vbg 3520 power supplies could be connected orseparated as shown or could be completely different with differentillumination device pinouts. Likewise, connections diagrams in LED lampor other applications could be implemented differently, as desired.

FIG. 39 illustrates one of many possible timing diagrams for the powersupplies Vr 3519 and Vbg 3520, and the LED current source outputs PWMr(red) 3647, PWMg (green) 3648, and PWMb (blue) 3649 in an FSC LCDbacklight. During start up, Vr 3519 goes high first and then Vbg 3520goes high, which enables reset generator 3644 in controller IC 3511 toproduce a valid /RST signal 3646 to start controller IC 3511 operatingfrom a known state. Controller IC 3511 then drives the red 3513, green3514, and blue 3515 LEDs sequentially by enabling each corresponding PWMand current source. When such PWM signal is shown to be high, no currentis drawn through the corresponding LED and no light is produced by thatLED. When such PWM signal is shown to be enabled (labeled EN indrawing), the corresponding PWM is enabled and pulsing current througheach such LED.

Because only one color LED is emitting at one time, photodiode 3512 canmonitor the light produced by each such LED on a continual basis andcontroller IC 3511 can continually adjust the drive current produced foreach such LED to maintain a precise color point and intensity.

The sequencing of the light colors shown in FIG. 39 are appropriate forFSC LCDs among other applications, which mix the red, green, and bluepixel data in time as opposed to in space. Conventional LCDs have awhite backlight and colors filters that produce the red, green, and bluelight for each pixel, which comprises liquid crystal sub-pixel elementsfor each color. The red, green, and blue pixel data then allowsdifferent amounts of light through each red, green, and blue sub-pixel.FSC LCDs have one liquid crystal pixel element that operates at leastthree times as fast to allow each color to be presented sequentially,which is mixed temporally by the eye.

FIG. 39 is one of many possible timing diagrams for power supplies andLED drive signals. For conventional displays and lamps, for instance,all LEDs would typically produce light at the same time to generate thenecessary white light. A different timing diagram could be used toenable the photodiode 3512 to monitor the light produced by each suchLEDs. For FSC LEDs, to reduce visual artifacts such as color breakup,the sequence of the different colored LEDs could be different. Forinstance, the color sequence could repeat over a number of video framesinstead of just one as shown. Additionally, methods such as so calledstenciling reduce color breakup by inserting a fourth field with allthree colors illuminated between each set of red, green, and bluefields. For both conventional and FSC displays, the timing of both thepower supply and LED drive signals could be significantly different.FIG. 39 is just one example.

FIG. 40 illustrates an illumination device 4080 that includes a photodetector 4081 and three LEDs, one for each of the colors red 4082, green4083, and blue 4084 as in illumination device 3510 but does not includea controller IC 3511. The photo detector 4081 can be, for example, asilicon photodiode, and the discussions below primarily use a photodiodeas the photo detector. However, as indicated above, the photo detector4081 can also be any light detecting device including but not limited toa silicon photodiode, a discreet LED, a light detecting LED or a lightdetecting LED integrated on the same die as one of the light emittingLEDs. As such, in some embodiments, the photo detector 4081 can beimplemented as a light detecting LED integrated on the same die as oneor more of the light emitting LEDs, if desired. The packageencapsulating such photo detector and LEDs comprises a six pin leadframe4085, an opaque plastic body 4086, and a clear plastic fill 4087 thatallows light from the LEDs to emit vertically from the package. Theleadframe 4085 comprises six pins for the signals Vr 4088, Vg 4089, andVb 4090 that connect to the anodes of such red, green, and blue LEDsrespectively, and for the signals LC 4091, PDC 4092, and PDA 4093. TheLC signal 4091 connects to the cathodes of all such LEDs, and PDC 4092and PDA 4093 connect to the photodiode 4081 cathode and anoderespectively. The backside of the illumination device 4080 should remainelectrically isolated in this example.

The photodiode 4081, and the green 4083 and blue 4084 LEDs can have bothcontacts on the top side of each such die with all anodes wire bondeddirectly to the corresponding pins. The LED cathodes are down bonded tothe lead frame which is then wire bonded to the LC 4091 pin. The surfaceanode connection on photodiode 4081 is wire bonded to the PDC 4093 pin.The red LED 4082 is shown to have a surface contact for the anode thatis wire bonded to the Vr 4088 pin and a backside contact for the cathodethat is electrically and mechanically connected to the lead frame.

FIG. 40 is one of many possible illumination devices 4080 that compriseLEDs and a photo detector to monitor the relative output power of eachLED to maintain a precise color point and intensity. For instance,illumination device could comprise more or less LEDs or additional photodetectors. The cathodes of the LEDs could have dedicated pins instead ofbeing connected together as shown or all the anodes could be common withthe cathodes pinned out separately. The photodiode cathode or anodecould share a common connection with one or more LEDs. The package couldbe mechanically completely different. The pins could be surface mount orthrough hole for instance. Further, as noted above, the photo detectordepicted as a photodiode can be any light detecting device, as desired,including but not limited to a silicon photodiode, a discreet LED, alight detecting LED or a light detecting LED integrated on the same dieas one of the light emitting LEDs.

FIG. 41 illustrates a possible LED controller IC 4100 that residesoutside the illumination device and provides the drive current to thered 4082, green 4083, and blue 4084 LEDs and monitors the light producedby such LEDs and the temperature using the photodiode 4081 andmeasurement block 4101. Such controller IC 4100 connects to N number ofillumination devices 4080 and maintains the proper illumination colorand intensity produced by all connected illumination devices 4080 overoperating conditions and lifetime. In this example, all the PDA 4093signals from illumination devices 4080 are tied together to the PDA 4114pin of controller IC 4100. Each illumination device PDC 4092 pin isconnected to a unique PDC pin on controller IC 4100 labeled PDC1 4115through PDCn 4116. Network interface 4102, timing and control circuitry4103, oscillator 4104, and color adjust block 4105 should be verysimilar or identical to such blocks comprising controller IC 3511.Likewise, PWM blocks 4106 through 4107 and current sources 4108 through4109 should be very similar or identical to such blocks comprisingcontroller IC 3511. The primary differences between controller IC 3511and controller IC 4100 include measurement block 4101, the number ofLEDs that can be driven, and the timing of how the LEDs are driven. Thecathodes of all three LEDs 4082, 4083, and 4084 of an illuminationdevice 4080 are connected to one current source 4108 through signal PWM14110. Up to N illumination devices 4080 can be connected to the Ncurrent sources identical to current source 4108 with current source4109 connected to signal PWMn 4111 representing the connection to theNth illumination device 4080. The LDO 3637 and reset circuitry 3644shown in controller IC 3511 are replaced with input pins VDD 4112 and/RST 4113. Din 4117 and Dout 4118 have similar functionality to Din 3521and Dout 3522 on Controller IC 3511.

FIG. 41 is one of many possible block diagrams for a controller ICconnecting to and controlling an illumination device 4080 comprising aphotodiode or other light detecting device, such as an LED, and LEDs inwhich the photodiode or other light detecting device, such as an LED,monitors the amount of light produced by such LEDs. For instance thecontroller IC could have LED driver circuitry for each color LEDindividually instead of controlling all three LEDs with one driver. Ifillumination device 4080 comprised a different number of LEDs, thencontroller IC 4100 would connect to that number of LEDs in eachillumination device.

FIG. 42 is one possible block diagram for the measurement block 4101that measures the photodiode 4081 current produced by LEDs 4082, 4083,and 4084 in all connected illumination devices 4100 and that uses suchphotodiodes 4081 to measure the temperature in each such connectedillumination device 4080. When LightEn signal 4228, which is controlsswitch 4220, is high and TempEn signal 4229, which controls switch 4221,is low, measurement block 4101 is configured to measure current inphotodiodes 4081 by shorting the photodiode 4081 anodes to ground andletting the selected photodiode 4081 cathode be controlled by amplifier4224. The current in the selected photodiode 4081 is forced throughresistor 4225 producing a voltage which is forwarded through mux 4226 toADC 4227.

When LightEn signal 4228 is low and TempEn signal 4229 is high,measurement block 4101 is configured to measure the temperature of thephotodiode in the selected illumination device 4080 by shorting thecathode of the selected photodiode 4081 to ground and forcing differentcurrents from current source 4223 through the selected photodiode.Current source 4223 supplies two different currents, I₀ and ten timesI₀, through the photodiode 4081 selected by mux 4222 and mux 4226forwards the resulting voltages to ADC 4227. The difference in the tworesulting voltages is proportional to absolute temperature.

FIG. 42 is one of many possible block diagrams for measurement block4101. As described for FIG. 37, the current induced in the photodiodesby the LEDs can be measured in a variety of ways. Likewise, thetemperature can be measured in a variety ways. For instance, twophotodiodes of different sizes could reside in the illumination device4080 and the voltage difference when applying the same current to bothphotodiodes can be measured.

FIG. 43 illustrates a possible connection diagram for multipleillumination devices with discreet photodiodes in a display backlight.Multiple instances of illumination device 4080 are connected to the Nnumber of LED drivers and photodiode measurement blocks on onecontroller IC 4100. Power Supply 4331 provides the Vr 4088, Vg 4089, andVb 4090 to all the illumination devices 4080 and provides a fixed powersupply to the video controller 4330 and the VDD 4112 power supply forthe controller IC 4100. The video controller 4330 provides the Din 4117and /RST 4113 signals to and accepts the Dout 4118 signal from thecontroller IC 4100. The PDA 4093 signals from all the illuminationdevices 4080 are connected to the PDA 4114 pin of the controller IC4100.

As described for FIG. 38, illumination devices 4080 can reside along theedges of an edge lit LCD or in an array behind the liquid crystal panelin a direct lit LCD. The video controller 4130 can communicateillumination data for each illumination device and can manage thecontroller IC 4100. Since the cathode of all the LEDs 4082, 4083, and4084 are connected together to one driver on controller IC 4100, suchconnection diagram only allows the intensity of light from color LED tobe controlled. Each color component is controlled individually byenabling the Vr 4088, Vg 4089, and Vb 4090 power supplies one at a time.

FIG. 43 is one of many possible connection diagrams for illuminationdevices 4080 and controller IC 4100. In displays that require moreillumination devices than one controller IC 4100 can support, multiplecontroller ICs 4100 can be serially connected through network interface4102 or video controller 4330 can connect directly to multiplecontroller ICs 4100. For conventional displays, illumination device 4080and controller IC 4100 could be configured to enable all LED colors tobe emitting simultaneously by tripling the number of drivers and theconnection diagram would differ accordingly.

FIG. 44 illustrates one of many possible timing diagrams for the powersupplies VDD 4112, Vr 4088, Vg 4089, and Vb 4090, the /RST signal 4113,and the LED current source output PWM1 4110 in an FSC LCD backlight.During start up, VDD 4112 goes high first and then /RST 4113 goes high,which starts controller IC 4100 operating from a known state. ControllerIC 4100 then signals to video controller 4330 and power supply 4331 tobegin sequencing the LED power supplies Vr 4088, Vg 4089, and Vb 4090.While each such LED power supply is high, controller IC 4100 drives theappropriate average current through each such LED. For instance, when Vr4088 is high, controller IC 4100 forwards the appropriate illuminationinformation for the red LED 4082 to the PWM 4106 and current source 4108to produce that appropriate light intensity from the red LED. Since thepower supplies, Vg 4089 and Vb 4090, to the green 4083 and blue 4084LEDs are low during this time, no current flows through such LEDs and nolight is produced.

Because only one color LED is emitting at one time, photodiode 4081 orother light detecting device, such as an LED, can monitor the lightproduced by each such LED on a continual basis and controller IC 4100can continually adjust the drive current produced for each such LED tomaintain a precise color point and intensity. Measurement block 4101sequentially and repetitively monitors the photodiodes 4081 connected topins PDC1 4115 through PDCn 4116.

FIG. 44 is one of many possible timing diagrams for power supplies andLED drive signals in an FSC display. For instance, the color sequencecould be different for different video frames and repeat over a numberof video frames instead of just one as shown. FIG. 44 is just oneexample. Likewise, timing diagrams in conventional displays or LED lampscould be implemented similarly or in a different manner, if desired. Insuch applications, the illumination device package could provideindependent pins for the LED cathodes so that all LEDs could be emitsimultaneously for some period of time and independently when emittedpower is measured. Other techniques could also be implemented ifdesired.

FIG. 45 is illustrates a possible block diagram for the color adjustmentblock 3636 in controller IC 3511, which is essentially repeated N timesin the color adjust block 4105 in controller IC 4100. For simplicity theremainder of this discussion will reference only illumination device3510 and not illumination device 4080 and controller IC 4100; however,the discussion is also applicable to these other embodiments. Further,for simplicity, this discussion assumes that a photodiode is being usedas the photo detector. However, as indicated above, the photo detectorcould be any light detecting device including but not limited to asilicon photodiode, a discreet LED, a light detecting LED or a lightdetecting LED integrated on the same die as one of the light emittingLEDs, as desired.

Color adjustment block 3636 receives the intensity data for the red3513, green 3514, and blue 3515 LEDs from timing and control circuitry3633, adjusts such values in matrix 4540, and forwards them to PWMs3638, 3639, and 3640. Matrix 4540 comprises coefficients determinedduring manufacturing of illumination device 3510 that are used tocompensate for variations in LED intensity and wavelength to produce thedesired color and intensity from the combination of red 3513, green3514, and blue 3515 LEDs at one temperature. The proper light color ismaintained during normal operation by continually comparing the ratio ofcurrents induced in photodiode 3512 by the red 3513 and green 3514 LEDsover the current induced in photodiode 3512 by the blue 3515 LED to thedesired ratios of such current determined during manufacturing, andadjusting the values forwarded to PWMs 3638 and 3639 through feedbackloops that include multipliers 4541 and 4543. The proper averageintensity of light produced by the combination of red 3513, green 3514,and blue 3515 LEDs is controlled periodically by comparing thetemperature adjusted current induced in photodiode 3512 by blue 3515 LEDto the desired such current determined during manufacturing, andadjusting the value forwarded to PWM 3640 with multiplier 4542.

During the manufacturing of illumination device 3510 when thecoefficients for matrix 4540 are determined, the currents induced inphotodiode 3512 by each LED 3513, 3514, and 3515 are measured and storedin registers 4544, 4546, and 4545 respectively. Likewise, thetemperature is measured and saved. During operation, the photodiodecurrents induced by the red 3513, green 3514, and blue 3515 LEDs arecontinually measured, digitized and stored in registers 4547, 4549, and4548 respectively. The ratios of actual photodiode currents induced bythe red LED 3513 and green LED 3514 over such current induced by theblue LED 3515 are determined by dividers 4550 and 4551 respectively.Such ratios of actual photodiode currents are compared to the ratios ofsuch desired photodiode currents determined during manufacturing andproduced by dividers 4552 and 4553. Since the photodiode currentsmeasured during manufacturing corresponded to particular intensity datafrom timing and control circuitry 3633, dividers 4554 and 4555, andmultipliers 4556 and 4558 adjust the ratio of such desired photodiodecurrents prior to be compared to the output of dividers 4550 and 4551 byadders 4559 and 4561. The differences between the desired photodiodecurrent and actual photodiode current ratios determined by adders 4559and 4561 are filtered by low pass filters 4562 and 4564 respectivelyprior to being applied to multipliers 4541 and 4543 respectively. Lowpass filters (LPFs) 4562 and 4564 are configured to ensure that thefeedback loop is stable.

Color adjustment block 3636 references the photodiode current induced bythe red LED 3513 and the green LED 3514 to the blue LED 3515 because theintensity of light produced by blue typically varies very little overtemperature. Color adjustment block 3636 compares ratios of photodiodecurrents instead of individual photodiode currents because thephotodiode response varies over temperature and other conditions. Bycomparing ratios of photodiode currents measured at the same time, anysuch variations cancel out and precise color can be maintained.

As blue LED 3515 ages, the light intensity produced for a given averagedrive current changes. Color adjustment block 3636 typically compensatesfor such changes in the blue LED once in a while, for instance duringpower up or on command, but could continually compensate. During suchcompensation, the actual photodiode current induced by blue LED 3515 ismeasured by measurement unit 3630 and the results are stored in register4548. Measurement unit 3630 also measures the temperature, the resultsof which temperature compensation block 4565 uses to scale the actualphotodiode current to the temperature during manufacturing when thedesired photodiode current stored in register 4545 was measured.Multiplier 4557 scales the output from register 4545 by the blue datafrom timing and control circuitry 3633, divider 4560 produces the ratioof multiplier 4557 output over the output from temperature compensationblock 4565, and the result of which is stored in register 4563.Multiplier 4542 adjusts the blue output from matrix 4540 prior toforwarding to PWM 3640.

FIG. 45 is one of many block diagrams for a color adjustment block 3636that maintains precise color and intensity of light produced by anillumination device 3510. Although color is preferentially controlled bycomparing a ratio of photodiode currents induced by different coloredLEDs at one time, for instance during manufacturing, to the ratio ofphotodiode currents induced by the same LEDs at a different time, colorcould be controlled by comparing actual photodiode currents to desiredphotocurrents. Such preferential color and intensity control circuitrycould be implemented in many different forms including software. Thefunctionality illustrated in FIG. 45 does not compensate for variationsin LED emission wavelength, which could be done by adjusting thecoefficients in matrix 4540. Likewise, the intensity adjustmentperformed by multipliers 4541, 4542, and 4543 could be done by adjustingthe coefficients in matrix 4540.

FIG. 46 is an example block diagram for matrix 4540 that can correct forvariations in both light intensity and wavelength produced by acombination of red, green, and blue LEDs 3513, 3514, and 3515 forinstance to produce uniform brightness and color from an array of LEDs.Matrix 4540 comprises memory 4670 that can store nine correctioncoefficients with three such coefficients for each color componentproduced. Coefficients Crr, Cgg, and Cbb would typically adjust forintensity variations in LEDs 3513, 3514, and 3515, while the remainingcoefficients (Crg, Crb, Cgr, Cgb, Cbr, Cbg) compensate for wavelengthvariations.

Memory 4670 can comprise SRAM, DRAM, FLASH, registers, or any other formof read-writable semiconductor memory. Such correction coefficients aretypically determined during manufacturing and remain unchanged duringoperation, however, such coefficients could be periodically modified bycontroller IC 3511 or any other processing element in a display or lampfor instance to adjust for changes in LEDs 3513, 3514, and 3515characteristics for instance over temperature or lifetime. If memory4670 does not comprise non-volatile memory such as FLASH, the correctioncoefficients should be loaded into such memory when powered up.

Multipliers 4671 scale the illumination data from timing and controlcircuitry 3633 by multiplying each color component by the correspondingcorrection coefficient. Such multiplication can be performed by discreethardware in bit parallel or bit serial form, in an embeddedmicrocontroller, or by any other means. Preferentially, one hardwaremultiplier comprising a shifter and an adder performs all ninemultiplications. Adder 4672 sums the multiplication results from thethree connected multipliers 4671 to produce the illumination dataforwarded to modulators 3638, 3639, and 3640. Such adders 4672 can beimplemented in hardware or software, or be performed bit parallel or bitserial.

FIG. 46 is just one of many possible block diagrams for correctionmatrix 4540. Likewise, correction matrix 4540 could reside elsewhere ina display, such as software in a graphics controller.

FIG. 47 is an example simplified block diagram of an LCD display 4780comprising of backlight 4781, diffuser 4782, polarizers 4783 and 4786,color filter 4784, and liquid crystal array 4785. Image pixel 4790 isexpanded to illustrate liquid crystal sub-pixel elements 4791, whichmodulate the amount of red, green, and blue light from color filterpixel element 4792, to produce a particular color and intensity fromsuch image pixel 4790. The backlight 4791 produces white light from oneor many light sources, such as LED 4793, that is made uniform across thedisplay by diffuser 4782. Polarizer 4783 only lets a particularpolarization of light through to color filter 4784, which produces red,green, and blue light. Liquid crystal array 4785 selectively rotates thepolarization of such light, which is then filtered by polarizer 4786 toproduce a color image of pixels 4790. Backlight 4781 typically comprisesone or more white LEDs 4793, but could comprise a color calibratedcombination of red, green, and blue LEDs.

FIG. 48 is an example simplified block diagram of FSC LCD 4800 thateliminates color filter 4784 by sequencing the red, green, and bluecolors through a single liquid crystal pixel element 4791 typicallythree times as fast as LCD 4780. Such a display typically costssignificantly less than and consumes much less power than LCD 4780,because the color filter is eliminated. Since the red, green, and bluecolors must be sequenced, white LED 4793 is replaced by red, green, andblue LEDs 3513, 3514, and 3515 in illumination device 3510. Currentsource 4794 is replaced with driver IC 3511 that sequentially enablesLEDs 3513, 3514, and 3515 by sequentially sinking current through thePWM signals PWMr (red) 3647, PWMg (green) 3648, and PWMb (blue) 3649respectively. To establish and maintain a precise average color andintensity produced by the combination of light from LEDs 3513, 3514, and3515, illumination device 3510 can comprise the circuitry and implementthe methods described herein. Illumination device 3510 illustrated inFIG. 48 illuminates many pixels 4791.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Fifth Embodiment

In certain exemplary embodiments, an improved illumination device usesthe components in an LED lamp to perform a variety of functions for verylow cost. The LEDs that produce light can be periodically turned offmomentarily, for example, for a duration that the human eye cannotperceive, in order for the lamp to receive commands optically. Theoptically transmitted commands can be sent to the lamp, for example,using a remote control device. The illumination device can use the LEDsthat are currently off to receive the data and then configure the lightaccordingly, or to measure light. Such light can be ambient light for aphotosensor function, or light from other LEDs in the illuminationdevice to adjust the color mix. Various embodiments are described withrespect to the drawings below. Other features and variations can also beimplemented, if desired, and related systems and methods can beutilized, as well.

In certain exemplary embodiments, an illumination device uses LEDs toproduce light and to provide bi-directional communication to acontroller that implements power saving features not possible withconventional lighting. The illumination device, for example, can beprogrammed with modulated light from a remote controller to turn on andoff, to adjust brightness or color, and to turn on or off in response tochanges in ambient light or timer count values. The LEDs that producethe illumination during normal operation are periodically used toreceive modulated light from a controller during short intervalsundetectable by the human eye. In response to a command from the remotecontroller, the illumination device can produce light modulated withdata. Additionally, when the remote controller is turned off and isexposed to sunlight, the LEDs in the controller can provide a tricklecharge current to maintain full battery power.

In certain aspects, the invention provides a system of an intelligentillumination device and, in some cases, a remote controller. Theillumination device, which is typically connected to an AC mains powersupply, can receive commands from the remote controller, which istypically battery powered, via light. The remote controller thenprograms the lamp for timer or photosensitive operation. For instance,at dusk the lamp could turn on and then go off, the light could come onwhen power is switched on and goes off a fixed time later, the lightcould come on and go off at fixed times, or the light could come on atdusk and off at dawn. Dimming could also be enabled or disabled, orcould be automatically adjusted based ambient light.

When turned on, the illumination device periodically turns off the LEDsto determine if any commands are being sent or to measure ambient light.The remote control synchronizes to these momentary “light off” periodsand sends a command if directed by the user. The commands can be on/off,dim, timer, photo cell, color, etc. When the light is turned off by theremote, ac power is still active. The device goes into a low power mode.When the remote turns the light on, the incident light can power theLEDs and enable the light to turn on. The light can also be turned offby removing AC power and turned on by turning AC power on. Cycling powerin a certain sequence can reset the light to a default state.

In certain embodiments, the illumination device uses the photosensitiveLEDs (i.e., the red LEDs) to detect received data or DC light during theintervals when the light output is momentarily turned off. Formulti-colored light, the illumination device can use a chain of thelongest wavelength LEDs (i.e., the red LEDs) to detect the output powerof the other colors. With two chains of the longest wavelength LEDs,each chain can measure the output power of the other, thereby enabling afeedback loop to control the output power of each color and the blendedcolor mix.

Once the illumination device (i.e., the “lamp”) is installed in anexisting socket that may or may not be connected to a dimming switch,the illumination device can be dimmed by the remote controller. Theremote controller sends commands to increment or decrement the outputlight level during the short “off” periods. The dimming function can beperformed by pulse width modulating the LED drive current at a switchingfrequency preferably locked to the switching regulator frequency or bysimply adjusting the LED drive current.

If photosensing is enabled, during the short light off periods, thelongest wavelength LED chain can be used to measure ambient light. To doso, the LEDs may be configured in photovoltaic mode, and produce avoltage proportional to incident light. If the voltage is above a levelspecified through a command, the lamp can turn off in response. If thevoltage drops back below the specified level, the lamp can turn on. Sucha mechanism enables the light to turn on at night and off during theday. In combination with a timer, the light can turn on at dusk and offafter a specified amount of time.

When the timer is enabled, the lamp can turn on and off at differenttimes of day or turn off after a specified amount of time after beingturned on. The lamp can be turned on by remote control, by power beingapplied through a switch, or by the photosensor function. In a mainsconnected application, the timer is synchronized to the AC frequency fora precise frequency reference.

When powered by a battery, the photosensitive LED chains can providetrickle current to re-charge the battery. A chain of 30 red LEDs (e.g.,in the CREE lamp) can produce nearly 1 mW of power that can keep are-chargeable battery charged in applications, such as emergency lights,that are not used often. For applications such as solar-powered,off-grid systems that are common in the developing world, the chargingcapability of the lamp can augment that of the solar panel.

As stated above, this fifth embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to the second, third, seventhand eighth embodiments can be used with respect to the intelligent LEDlights described in this fifth embodiment. Further, the communicationtechniques described with respect to this fifth embodiment can be usedwith respect to the other embodiments, if desired.

Turning now to the drawings, FIG. 49 is one example of an intelligentillumination device system 4910 that comprises the illumination device4911 and the remote controller 4912. The remote controller 4912 ispreferably battery powered like a flashlight or TV remote control and isused to program the illumination device 4911 with modulated light. Whenthe illumination device 4911 is powered preferably by the AC mains of anelectrical socket (e.g., an Edison base socket), the illumination device4911 can be controlled by the remote controller 4912. When theillumination device 4911 is enabled to produce light (i.e., “turned on”or “producing light”), the illumination device 4911 briefly andperiodically stops emitting light to detect commands from the remotecontroller 4912 or ambient light from the environment, or to calibratecolors in a multi-colored illumination device 4911. When theillumination device 4911 is powered by the AC mains, but is not enabledto produce light (i.e., “turned off”), the illumination device enters alow power state. Commands from the remote controller 4912 can still bedetected by the illumination device 4911 in this state. The illuminationdevice 4911 responds to the remote controller 4912 by momentarilyproducing light modulated with data. To reset the illumination device4911 to a default state, power to the illumination device 4911 is cycledin a specific sequence.

FIG. 49 is just one example of many possible intelligent illuminationdevice systems. For example, the illumination device 4911 could bepowered with a battery or the remote controller 4912 could be powered bythe AC mains. In another example, if the illumination device isprogrammed when it is designed or produced, no remote controller 4912 isneeded. Examples of pre-programmed devices include pre-configured nightlights, and lights that automatically turn of perhaps 1 hour (or otherdelay) after being turned on. In such case, the functionality of theillumination device may be reduced.

In another example, light from the remote controller 4912 could power anun-powered illumination device 4911 with light while programming. Forinstance, a consumer could buy a light bulb replacement including thisremote controller. The consumer could then hold the bulb to the remoteand configure it to turn off 35 minutes after being turned on, then takethe programmed bulb and screw in a socket somewhere. Without thisself-powered variant, the bulb would need to be screwed into anenergized socket in order to program it, which may be possible, butstill perhaps less convenient.

In a further example, the remote controller battery could be charged bysunlight or ambient light when not in use. Additionally, multipleillumination devices 4911 could communicate with each other. Forexample, various governments have recently introduced mandates thatcertain buildings must have intelligent lights that automatically turnon and off based on whether or not people are present. Some largelighting companies provide systems consisting of lamps with motiondetectors and 900 MHz RF transceivers. When one lamp in a room detectsmotion, it tells the rest of the lights to turn on. The two main issueswith this approach are: (1) the lights are expensive, and (2) the RFsignal passes through walls to other rooms with no people. The devicesdescribed herein could communicate with each other via light which: (1)does not require the expense of the RF circuitry, and (2) does not gothrough walls. Additionally, functions like dimming or color controlcould benefit from lamps communicating with each other. For example, auser could program one lamp, and that lamp then reconfigures the otherlamps. Additional applications could be security where two lampsconstantly communicate with each other. If an intruder passes betweenthem and momentarily blocks the light, the lamps detect this andbroadcast info to other lamps in the building in sort of a daisy chainway to a central security system.

FIG. 50 provides Table 2 that includes an example list of commands 5014for the illumination device 4911 that enable the remote controller 4912to turn the illumination device 4911 on and off, adjust the outputpower, and change the color to one of three different settings.Additionally, the illumination device 4911 can be configured toautomatically turn on in response to a time of day counter reaching aparticular count or ambient light dropping below a certain level, and toautomatically turn off after a timer reaching a particular count fromwhen the illumination device 4911 is turned on or ambient light risingabove certain level. In this example, the color mix is alwaysautomatically measured and adjusted to a specific setting. The exampleset of commands 5014 can use 4 bits to produce hex codes 5013.

Preferably, the hex codes 5013 are preceded by a synchronization patternand followed by parity to produce an 8 bit transfer sequence.Additionally, the commands that set a time must be followed with theactual time. Since there are 1440 minutes in a day, a time with oneminute resolution requires 11 bits, which could be sent in twosuccessive transfers after the command.

Table 2 is just one example of many possible sets of commands 5014 andhex codes 5013. For instance, in a multi-color light each individualcomponent could be dimmed or color calibration could be enabled anddisabled. As another example the time of day counter could count days ofthe week as well. The illumination device 4911 could have a subset ofthese functions or could have a variety of other functions such asstrobing or continuous color variation. Additionally, illuminationdevice 4911 status and register contents could be read. Further, theassignment of hex codes 5013 to commands 5014 could be completelydifferent and could contain more or less bits depending on the number ofcommands 5014.

FIG. 51 is an example timing diagram for communicating commands 5014between the illumination device 4911 and the remote controller 4912 whenthe illumination device 4911 is producing light. Pulse width modulatedlight PWM 5120 from the illumination device 4911 is periodicallyinterrupted by gaps 5121 when no light is produced. The gap period 5122in this example is one second. The gap time 5123 is equal to one halfthe mains period or 8.33 mSec at 60 Hz. The remote controller 4912synchronizes to gaps 5121 in the PWM 5120 light from the illuminationdevice 4911 and can send commands CMD 5124 during gaps 5121. When a CMD5124 is sent from the remote controller 4912 and is properly received bythe illumination device 4911, the illumination device 4911 provides aresponse RSP 5125 immediately after CMD 5124. The remote controller 4912may preferably be narrowly focused (much like a flashlight) to assist auser in directing the remote commands to a particular illuminationdevice in a room with multiple such illumination devices. The user couldsee the light beam and shine it directly on one light. This would focuslight from the remote on the illumination device and light from theillumination device on the detector in the remote.

In this example, the light from the illumination device 4911 is pulsewidth modulated at 16 times the mains frequency or 960 Hz for 60 Hz AC,to enable dimming without changing LED wavelengths. At full brightness,the off time is very short or non-existent and at low light levels, theon time is short. The frequency of the pulses stays fixed. To preventthe remote controller 4912 from losing synchronization with theillumination device 4911, the last pulse from the illumination device4911 before a gap 5121 is preferably not reduced below a minimum widththat the remote controller 4912 can detect.

In another example, the one second gap period 5122 can be shortened to200 msec for instance, after the illumination device 4911 and remotecontroller 4912 communicate a first CMD 5124 so that successive commandscan be communicated faster. This may be important for dimming sincethere may be many power level steps between low and high power. Once theremote controller 4912 stops sending commands, the gap period 5122widens back to one second intervals.

When the illumination device 4911 is not producing light, the remotecontroller 4912 does not detect gaps 5121 and can send commands CMD 5124at any time. The protocol shown in FIG. 51 remains the same except thatthe illumination device 4911 is not outputting PWM 5120 light before andafter the transaction.

During gaps 5121 when commands CMD 5124 are not sent or when theillumination device 4911 is not producing light, the illumination device4911 can measure ambient light. The ambient light level is subtractedfrom the received light when commands CMD 5124 are sent and is used todetermine when to turn the illumination device 4911 on or off whenphoto-sensor functionality is enabled. More specifically, when theillumination device is receiving commands, the background or ambientlight produces a DC offset in the optically induced voltage across theLEDs (or photodiode). This DC offset can be eliminated by measuring theoptically induced voltage during gaps 5121 when no commands are sent,and subtracting it from the induced voltage when receiving commands.Alternatively, the receiver in the illumination device can high passfilter the induced voltage to remove the DC offset. Since the data rateis low, the receiver may use a digital filter for DC blocking (andequalization). If the DC offset is known prior to receiving a command,the initial state of the digital filter can be set accordingly, andreduce the settling time. When photosensor functionality is enabled,ambient light is measured during gaps 5121 when the illumination deviceis producing light, and measured all the time when not producing light.

Additionally, in a multi-color illumination device 4911, the intensityof each individual color can be measured during gaps 5121 or when theillumination device 4911 is not producing light. For instance, when theillumination device 4911 is turned on, the illumination device 4911 canbriefly measure the intensity of each color before producing the desiredlight. Then periodically as the illumination device warms up forinstance, the color components can be measured during gaps 5121.

FIG. 51 is just one example of many possible timing diagrams. The gapperiod 5122 and gap time 5123 could be substantially different dependingon the applications. The response RSP 5125 can be sent at differenttimes or not at all. The commands CMD 5124 could even be sent during theoff times of the PWM cycle and responses RSP 5125 could be variations inPWM duty cycle. To provide additional error protection, commands CMD5124 could be repeated one or more times before taking affect. Manydifferent timing diagrams and communication protocols could beimplemented. For an illumination device 4911 that is powered by thelight from the remote controller 4912 instead of a battery or AC mains,the protocol can include significant illumination durations in order tostore sufficient charge on a capacitor for instance to power theillumination device 4911 and to communicate data.

FIG. 52 is an example timing diagram illustrating the bit levelcommunication between the illumination device 4911 and the remotecontroller 4912 when the illumination device 4911 is producing light.Communication begins with the illumination device 4911 stopping the PWM5120 output. The illumination device synchronization IDSYNC 5230 pulseis the last PWM pulse produced by the illumination device 4911 prior toa gap 5121. The width of IDSYNC 5230 is greater than the minimum pulsewidth detectable by the remote controller 4912. Other synchronizationsequences, such as short series of pulses, may also be produced beforeeach gap 5121. The CMD 5124 from the remote controller 4912 comprises asynchronization pattern SYNC 5231 of 3 ones, a hex code 5013, and aneven parity bit P 5232 that are biphase encoded. In this example, thecommand 5014 is “light off”. If the illumination device 4911 receivesthe CMD 5124 properly, the response RSP 5125 comprises the same biphaseencoded SYNC 5231, hex code 5013, and parity P 5232 that comprised theCMD 5124. When the illumination device 4911 is not producing light, theprotocol shown in FIG. 52 remains the same except that the illuminationdevice is not outputting PWM 5120 light (nor IDSYNC 5230) before andafter the transaction.

FIG. 52 is just one example of many possible bit timing diagrams.Instead of biphase encoding, the protocol could use any one of many wellknown coding schemes such 4b5b, 8b10b, or NRZ. The SYNC 5231 could havea wide variety of lengths and sequences including none at all. The hexcodes 5013 could have more or less bits and parity P 5232 could be evenor odd, more than one bit, or none at all. CRC codes could be used forerror detection. For an illumination device 4911 that is powered bylight from the remote controller 4912, the protocol could besubstantially different. In particular, it may be necessary to transmitdata one bit at a time from the illumination device 4911 to the remotecontroller 4912 with the remote controller 4912 emitting light tore-charge a capacitor on the illumination device 4911 for instancebetween bits sent from the illumination device 4911. Useful transceivertechniques for so doing are described in U.S. patent application Ser.No. 12/360,467 filed Jan. 27, 2009 by David J. Knapp and entitled “FaultTolerant Network Utilizing Bi-Directional Point-to-Point CommunicationsLinks Between Nodes,” and in U.S. patent application Ser. No.12/584,143, filed Sep. 1, 2009 by David J. Knapp and entitled “OpticalCommunication Device, Method and System,” each of which is herebyincorporated by reference in its entirety.

FIG. 53 is an example block diagram for an exemplary illumination device4911 that comprises an EMI filter and rectifier 5341, an AC to DCconverter, a voltage divider, an integrated circuit IC 5354, and the LEDchain 5353. The EMI filter and rectifier 5341 produces a full waverectified version of the AC mains VAC 5340, and minimizes both transientdisturbances on the mains from affecting the rectified power, andswitching noise in the illumination device 4911 from affecting themains. The voltage divider comprises resistors R 5342 and R 5343 andproduces signal S 5357 that is a reduced voltage version of therectified mains signal for IC 5354. The AC to DC converter includesinductors 5344 and 5345 (also referred to herein as inductors L 5344 andL 5345), capacitors 5346 and 5347 (also “capacitors C 5346 and C 5347”),diode 5348 (also “diode D 5348”), the N-channel switch transistor 5349(also “switch N 5349”), and the power controller 5362 on integratedcircuit 5354 (IC 5354). This example shows LED chain 5353 comprising ofLED 5350, LED 5351, and LEDn 5352, with the dashed line between LED 5352and LEDn 5353 indicating that LED chain 5353 can include many LEDs. Thisarchitecture is typical for monochrome light or white light produced byblue LEDs with a phosphor coating. A multi-color illumination devicetypically would have separate LED chains for each color.

IC 5354 includes memory and control 5360, PLL and timing 5361, powercontrol 5362, receiver 5363, and output driver 5364. Memory and control5360 includes non-volatile memory for storing configuration information,such as enabling the timer or photo-sensor, and volatile (ornon-volatile) memory for settings such as dimming. Memory and control5360 also includes logic that manages the transfer of data with theremote controller 4912, produces the pulse width modulated (PWM) LEDdrive signal S 5359, and implements the timers and state machines thatcontrol the overall function of IC 5354 and the illumination device4911.

PLL and timing 5361 includes a phase locked loop that produces a highfrequency clock that is phase locked to S 5357 when the illuminationdevice is powered. The voltage divider comprising of R 5342 and R 5343provides a low voltage version of the rectified mains voltage S 5357that does not exceed the voltage rating of IC 5354 and that the PLLlocks to. All other circuitry on IC 5354 is synchronized to the PLL andtiming 5361 outputs (not shown).

PLL and timing 5361 enables the illumination device 4911 to maintain aprecise time base for time of day timer functionality by locking to themains frequency. Likewise, gap period 5122 and gap time 5123 can beprecisely aligned to VAC 5340 timing. Such timing could enable multipleillumination devices 4911 to synchronize and communicate directlybetween each other with light. For example, multiple illuminationdevices (i.e., “IDs”) can sync to each other by first looking for GAPS(e.g., gaps 5121) just before producing light. If proper GAPs are found,the illumination device syncs to them. If no gaps are found, there isnothing to sync to and the illumination device effectively becomes atiming master that other illumination devices lock to when turned on.Such an illumination device preferably should also be able to detect ifsync is lost and to re-lock. It is further noted that additionalembodiments for illumination devices and systems as well as for visiblelight communication systems and methods are also described with respectto the fourth and sixth embodiments described herein. It is furthernoted that display related systems and methods, display calibrationsystems and methods, and LED calibration systems and methods are alsodescribed with respect to the first, second, third, seventh and eighthembodiments described herein.

When VAC 5340 is turned off, capacitor C 5347 can maintain power to IC5354 for some period of time. If VAC 5340 is turned off and on withinthis time, IC 5354 can remain powered. To reset the illumination device11 to a default state, VAC 5340 can be turned off and on a number oftimes for specified amounts of time. For instance, the reset sequencecould be 3 short off and on intervals, followed by 3 longer off and onintervals, and followed finally by 3 more short off and on intervals.PLL and timing 5361 monitors signal S 5357, signals IC 5354 to enter alow power state when signal S 5357 stays low, and measures the timebetween short VAC 5340 off and on periods. When PLL and timing 5361detects the proper VAC 5340 off and on sequence, IC 5354 is reset to adefault state.

Power control 5362, together with the external components inductors L5344 and L 5345, capacitors C 5346 and C 5347, diode D 5348, and switchN 5349, and current sensing feedback from output driver 5364, implementthe AC-to-DC converter function. The configuration implemented is thewell known Single Ended Primary Inductor Converter (SEPIC). Switch N5349 is turned on and off by power control 5362 at a relatively highfrequency such as 1 MHz, with the duty cycle varying to produce thedesired current through LED chain 5353. When switch N 5349 is closed,the current from L 5344 and L 5345 is pulled through switch N 5349 andcharge stored on the capacitor C 5346 provides current to LED chain5353. When switch N 5349 is open, the current through inductors L 5344and L 5345 flows through the diode D 5348 and to LED chain 5353 and C5347.

Power control 5362 compares voltage feedback signal Vfb 5365 from outputdriver 5364 to an internal reference voltage to produce an error signalthat adjusts the duty cycle of the control signal S 5358 that is coupledto switch N 5349. The signal Vfb 5365 is produced by LED chain 5353current flowing through a small resistor in output driver 5364 (notshown). When LED chain 5353 is turned off, Vfb 5365 becomes a divideddown version of V+ 5355, which occurs when receiving data and during thePWM dimming off times. A control loop adjusts the feedback divider tomaintain V+ 5355 at the same voltage as when LED chain 5353 is on.

When output driver 5364 turns the current to LED chain 5353 on or off,large voltage transients can occur on V+ 5355 before the power control5362 can adjust to the new duty cycle of signal S 5358. When the LEDchain 5353 current is turned off, V+ 5355 will go high until the dutycycle of S 5358 is reduced, and when the LED chain 5353 current isturned on, V+ 5355 will go low until the duty cycle of S 5358 isincreased. To minimize such transients; power control 5362 receivesinformation from memory and control 5360 in advance of when such changeswill occur and adjusts S 5358 duty cycle the instant such a change isneeded. Just prior to the output driver 5364 turning the LED chain 5353current off, power control 5362 measures S 5358 duty cycle and storesthe result. This duty cycle is restored instantly the next time LEDchain 5353 current is turned off to prevent V+ 5355 from spiking high.Likewise, the S 5358 duty cycle is measured when the LED current isturned on, and the result is stored, and then restored to prevent V+5355 from spiking low.

Output driver 5364 turns LED chain 5353 current on and off with a switchconnected to ground (not shown). Current flows from V+ 5355 to groundthrough LED chain 5353 and the switch, when the switch is on, and nocurrent flows when the switch is off. A small resistor in series withthe switch produces Vfb 5365 when the switch is on. When the switch ison, a control loop compares the output of a variable voltage dividerfrom V+ 5355 to Vfb 5365 and adjusts the divider until the output equalsVfb 5365. When the LED chain 5353 current is turned off, the V+ 5355voltage divider loop is also turned off and the voltage divider remainsfixed. While the LED chain 5353 current is off, this divided version ofV+ 5355 is forwarded to power control 5362 through Vfb 5365.

Receiver 5363 can receive data from the remote controller 4912, when theLED chain 5353 current is turned off by output driver 5364. Modulatedlight from remote controller 4912 is converted to a voltage signal S5359 by LED chain 5353, which operates in photo-voltaic mode as in asolar panel. Receiver 5363 high pass filters S 5359 to block the DCcontent from ambient light and to cancel the low bandwidth of thephoto-voltaic LED chain 5353. Such bandwidth typically supports up to 1k bits per second (1 kbps), but with the proper equalization filter thedata rate can be increased by 10 times or more. To support the protocolin FIGS. 51 and 52, 2 kbps are needed. Receiver 5363 comprises an A/Dconverter and a digital filter to equalize signal S 5359. Timingrecovery is not needed since the data is sent from the remote controller4912 synchronously to the AC mains frequency that IC 5354 is locked to.The output of the digital filter is simply sampled at the appropriatetimes.

When the illumination device 4911 is not producing light, the remotecontroller 4912 detects the absence of gaps 5121. Since the remotecontroller 4912 is not synchronized to the gaps 5121 from theillumination device 4911, and since the remote controller 4912 isbattery powered, data from the remote controller 4912 is asynchronous tothe timing in the illumination device 4911. Provided the remotecontroller 4912 has a precise oscillator, such as a quartz crystal, theremote controller 4912 and the illumination device reference clocks willtypically be within a couple hundred parts per million of each other.The illumination device 4911 resets a timer clocked at high frequency onthe falling edge of the third SYNC 5231 pulse and uses this timer tosample received data and produce transmitted data. The drift between thetwo reference clocks over the 16 msec period of one transfer isinsignificant.

The illumination device 4911 measures ambient light during gaps 5121,and also when the illumination device 4911 is not producing light, bymeasuring the average voltage of signal S 5359 with the A/D converter inreceiver 5363. The A/D converter should be architected to have small DCerrors, such as the well known chopper stabilization architecture, tomeasure very low light levels.

FIG. 53 is just one example of many possible illumination device 4911block diagrams. For example, an illumination device 4911 architecturefor multi-colored light could comprise of an LED chain 5353 and outputdriver 5364 for each component color. Example color combinations couldcomprise of red, green, and blue, or of red, yellow, green, and blue, orof red and white. During gaps 5121, and also when the illuminationdevice 4911 is not producing light, the lower light frequency LEDs canmeasure the light intensity of each other and of the higher lightfrequency LEDs. For instance, in a red and white illumination device,during gaps 5121 for instance, the white LED chain could produce lightand the red LED chain could be connected to the receiver and couldmeasure the light power. If the red LEDs are organized in two separatechains with separate output drivers, during gaps 5121 for instance, onered LED chain could measure the light power of the other. By measuringthe light power from each LED chain, the illumination device couldadjust the current to the different LED chains to maintain a specificcolor point for instance over LED variations, temperature variations,and LED lifetime. A single receiver 5363 could be shared and connectedat different times to different LED chains, or multiple receivers 5363could be implemented.

Another example illumination device 4911 block diagram for anillumination device that can be powered by the remote controller 4912during configuration could comprise a second very low power receiver.The second receiver could be powered by an LED chain receiving modulatedlight and could store configuration information in non-volatile memory.The average voltage induced across the LED chain by light is typicallysignificantly lower than the voltage necessary to produce light from thesame LED chain. The induced voltage could be stored across capacitor C5347 and a smaller segment of the LED chain 5353 could be connected tooutput driver 5364 to emit responses to the remote controller 4912. Thecommunication protocol to configure an illumination device 4911 when notpowered could be different from FIG. 51 to enable capacitor C 5347 to bere-charged after each emitted light pulse. Useful techniques for sodoing are described in the aforementioned U.S. application Ser. No.12/360,467 and No. 12/584,143.

The block diagram for an illumination device 4911 that is powered by abattery instead of the AC mains would have a battery and potentially adifferent type of switching power supply such as the well known buck,boost, boost buck, or flyback. With a re-chargeable battery, ambientlight or sunlight incident on the LEDs could produce power to re-chargethe battery. A block diagram for such an illumination device 4911 couldhave a second power control 5362 that manages the battery charger. Anillumination device powered by the AC mains could also have any of awide variety of different AC-DC converters, such as the boost buck orflyback. Such an illumination device could also have a back upre-chargeable battery that enables the illumination device to maintainthe time of day counter when power goes off. The timing for theillumination device 4911 could also be based on a local crystaloscillator instead the mains frequency for instance.

As a further example, the block diagram for an illumination device thatuses a silicon photodiode instead of LEDs for instance for receivingdata would have the receiver 5363 connected to the photodiode instead ofLED chain 5353. Such architectures would be particularly useful forillumination devices that only use phosphor coated white LEDs that donot operate well in photo-voltaic mode. The silicon photodiode couldreceive commands 5124 from the remote controller 4912, measure ambientlight, and measure emitted light from the LED chain.

Multiple illumination devices could also communicate with each other. Inthis example, an illumination device 4911 could execute a protocol tosynchronize to other illumination devices and to arbitrate fortransmission bandwidth. When turned on, an illumination device 4911could monitor the ambient light, search for gaps 5121 with the propergap period 5122 and gap time 5123, and synchronize to the gaps 5121 iffound. If all the illumination devices are connected to the AC mains,then very precise synchronization is possible. Illumination devicescould arbitrate for bandwidth according any one of many well knownarbitration protocols. For instance, if two illumination devicestransmit at the same time, both illumination devices detect thecollision and wait a random amount of time before trying to communicateagain. As another possibility, a CMD 5124 could include a priority codethat indicates in the case of a collision, which illumination devicestops transmitting.

As used herein, an illumination device is assumed to produce a generallight, usually of a human-perceivable nature, but possibly infrared orsome other wavelength. An illumination device enabled to produce light(i.e., “turned on”) may be thought of as being set to an “on-state”(i.e., having its illumination state set to an on-state), even though,as described above, there may be very short periods of time during whichthe light source is momentarily turned “off” and is not actuallyemitting light, such as during the gaps, and during the off-times in aPWM signal. The on-state and off-state of the illumination device shouldbe clear in the context described above and not confused with the on andoff status of the actual light source.

An illumination device may be set to an on-state or off-state by any ofseveral events, such as application/removal of power to the illuminationdevice (such as by energizing the light socket into which theillumination device is inserted), by a timer event, by ambient lightcontrol, and by a remote command.

Exemplary block diagrams are depicted herein. However, other blockpartitionings of an illumination device may be provided. As used herein,an illumination device attribute may represent an operational state or aconfiguration parameter of the illumination device. Examples include theillumination state, timer settings, delay settings, color settings foreach of one or more light sources within the illumination device,photosensing mode settings, dimmer settings, time-of-day, etc.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Sixth Embodiment

Systems and methods for visible light communication are disclosed. Inpart, illumination devices and related systems and methods are disclosedthat can be used for general illumination, lighting control systems, orother applications. The illumination devices utilize one or moresynchronized timing signals to synchronize, preferentially to the ACmains, so as to produce time division multiplexed channels in whichcontrol information can be communicated optically by the same lightsource that is producing illumination. Such illumination devicespreferentially comprise LEDs for producing illumination, transmittingdata detecting ambient light, and receiving data, however, other lightsources and detectors can be used. The physical layer for suchcommunication can be used with a variety of protocols, such as ZigBee,from the Media ACcess (MAC) layer and higher. Various embodiments aredescribed with respect to the drawings below. Other features andvariations can also be implemented, if desired, and related systems andmethods can be utilized, as well.

In certain embodiments, the visible light communication techniquesdescribed herein can be used in combination with existing electronicsfor LED lights to implement a variety of advantageous lighting controlsystems and features, such as remote control, daylight harvesting,scheduling, and occupancy sensing in the light are possible at verylittle additional cost. These lighting control systems further allow aplurality of illumination devices to communicate with each other, remotecontrollers, and a central controller. Further, the techniques describedherein could also be used by a single illumination device andcontroller, or other devices and applications, as desired. Inparticular, an AC mains powered controller with a light source that isnormally off could communicate information, such as dimming level andcolor settings, to one or more LED lamps. In contrast with thetechniques described herein, control of conventional lighting istypically performed by separate electronic units that communicate witheach other over wires or radios, which add cost and complexity.

Illumination devices described herein preferentially comprise phaselocked loops (PLLs) that phase lock to the AC mains and produce thesynchronized timing signals for operating the devices. Since otherillumination devices in the lighting systems for instance phase lock tothe same AC mains signal, all such devices have precisely the sameinternal timing. With such synchronized timing, communication channelscan be formed during which all devices can communicate. Likewise, sincethe bit level timing of data communication within such channels isprecisely synchronized, data recovery within a receiver is substantiallyeasier since the received data timing is known.

A communication channel is a timeslot that preferentially spans afraction of an AC mains period (16.67 mSec for 60 Hz) during which allthe members of a group of devices stop producing illumination. Higherlayers in a communication protocol, such as ZigBee, can dynamicallyassign individual devices to communicate on different channels. Duringsuch timeslots information can be communicated optically between suchmembers when one member produces light modulated with data. During suchtimeslots when data is not being communicated, ambient light can bemeasured for daylight harvesting applications and for improving receiversensitivity.

Preferentially, the illumination devices comprise LEDs for illuminationand for transmitting and receiving data to minimize cost and maximizereceiver sensitivity. Because white LEDs that comprise a blue LEDcovered with a phosphor have poor sensitivity to received light,preferentially the illumination devices comprise LEDs with differentcolors to produce the desired white light. Possible combinations includewhite and red, or red, yellow, green, and blue, but could include anycombination or even a single color provided at least one LED in theillumination device is preferably not phosphor coated. Preferentially,the illumination devices comprise red LEDs for best receiversensitivity. The additional cost of controlling multicolored LEDs can bereduced or eliminated in lamps that combine the systems and methodsdescribed herein with those described in additional embodiments asdescribed herein for calibrating devices using LEDs such as thosedescribed herein with respect to the second embodiment, the thirdembodiment, the seventh embodiment and the eighth embodiment. Theseembodiments describe in part techniques to precisely control the colorof light produced by combinations of different colored LEDs, such aswhite and red, or red, yellow, green, and blue, and can do so withoutthe need for additional photo-detectors or temperature sensors therebymaking such implementations more cost effective.

The messages in a communication channel are preferentially sent a fewbytes at a time in successive timeslots over a complete physical layerdata frame. Such a data frame comprises a MAC layer data framesuperseded by additional physical layer information with most of thephysical layer data frame scrambled by well known methods to remove DCcontent. The MAC layer data frame can conform to any protocol includingZigBee.

The systems and methods disclosed herein address problems with priorsystems in part by providing physical layers for lighting controlsystems for reduced costs and/or relatively insignificant additionalcosts. Advantageously, the illumination devices and other devices in thelighting system described herein can communicate using the devicesalready needed for illumination.

As stated above, this sixth embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to the second, third, seventhand eighth embodiments can be used with respect to the visible lightcommunication systems and methods described in this sixth embodiment.Further, the communication and synchronization techniques described withrespect to this sixth embodiment can be used with respect to the otherembodiments, if desired.

Turning now to the drawings, FIG. 54 is one example of a lighting system5410 comprising illumination devices 5411, AC mains 5413, and optionallyremote controller 5412 that uses visible light for both illumination andcommunication. The illumination devices 5411 preferentially compriseLEDs to produce light for both lighting and communicating, and arepreferentially connected and synchronized to the AC mains 5413. Timingcircuits in the illumination devices 5411 lock to the AC mains 5413frequency and produce periodic intervals during which all illuminationdevices 5411 do not emit light for illumination and may communicatedata. The periodic interval rate is sufficiently high for humans tosimply perceive continuously light. The data communicated preferentiallycomprises information to control the illumination devices, but couldcomprise any digital information.

Optional remote controller 5412 can be AC mains 5413 or battery poweredand preferentially comprises at least one LED for producing visiblelight to communicate with the illumination devices 5411. If remotecontroller 5412 is AC mains powered, timing circuits lock to the ACmains 5413, which synchronizes remote controller 5412 with theillumination devices 5411 and enables optical communication. If remotecontroller 5412 is not connected to the AC mains 5413, remote controller5412 monitors the light produced by illumination devices 5411 and locksto the periodic light off intervals to enable communication. If theillumination devices are turned off and are not producing light, remotecontroller 5412 can communicate with illumination devices 5411 anytime.

The network protocol stack for communicating information, with theexception of the physical layer, preferentially follows the well knownZigbee standard, but could follow many different protocols. While theZigbee physical layer can use multiple different radio frequencycommunication channels, the embodiments described herein can communicateover multiple visible light communication channels that are shifted intime relative to each other and the AC mains signal. Both physicallayers can interface to the Zigbee Media ACcess or MAC layer.

FIG. 54 is just one example of a lighting system using visible light forsynchronous communication. For instance, any number of illuminationdevices 5411 could be supported. Some illumination devices 5411 could beAC mains 5413 powered, while others are battery powered. More or lessremote controllers 5412 could be supported. A variety of other AC mains5413 or battery powered devices such as switches, dimmers, appliances,and even computers could communicate under the techniques describedherein. Likewise, illumination and other devices could synchronize inmany different ways. For instance a dedicated wire, RF channel, or someother communication channel could provide such synchronization signal.Additionally, devices could synchronize to other devices alreadycommunicating by monitoring the light being produced by such otherdevices, and locking to communication gaps in such light.

FIG. 55 is an example timing diagram for communicating betweenillumination devices 5411 in lighting system 5410 that illustrates therelationship between the AC mains 5413 timing that is typically 50 or 60Hz, four different communication channels 5524 labeled Channel 0 throughChannel 3 that comprise PWM time 5520 and communication gap time 5521,and the gap timing that comprises four data bytes 5522 labeled BYTE 0through BYTE 3. During PWM time 5520, illumination devices 5411 canproduce light for illumination and during gap time 5521 illuminationdevices 5411 can communicate. In this example, channels 0 through 3provide gap times 5521 that have different non-overlapping phasesrelative to the AC mains timing, which provide four independentcommunication channels.

The gap period for each channel 0 through 3 in this example is equal toone over the AC mains frequency and comprise alternating PWM 5520 andgap 5521 times. During PWM 5520 times, light from an illumination device5411 can be on continually to produce a maximum brightness or PulseWidth Modulated (PWM) to produce less brightness. During the repetitivegap 5521 times, data can be sent from any device to any or all otherdevices. In this example, the gap time is one quarter of the AC mains5413 period and enables four data bytes 5522 to be communicated at aninstantaneous bit rate of 60 Hz times four times 32 or 7.68K bits persecond and an average bit rate of 1.92K bits per second.

Higher layers in the Zigbee or other protocol stack select which channelis used for communication between which devices. For instance, a groupof illumination devices 5411 that are physically located over asufficiently wide area such that some illumination devices 5411 cannotcommunicate directly with each other can be divided into multiple groupsof illumination devices 5411 with each group configured to communicateon a different communication channel. Communication between such groupscould pass through an illumination device that communicates on twochannels for instance.

FIG. 55 is just one of many possible timing diagrams for lighting system5410. For instance, gaps 5521 could occur multiple times per AC mains5413 period or once per multiple AC mains 5413 periods. The gap 5521time could comprise a larger or smaller percentage of the AC mains 5413period, and the number of bytes 5522 communicated within a gap 5521 timecould be more or less than 4 including fractions of bytes. The number ofchannels could be more or less than 4 depending on the relationshipbetween the gap 5521 time and period and the AC mains 5413 timing.

FIG. 56 illustrates the contents of data frame 5630 comprising a fourbyte preamble 5631, a start byte 5632, a frame length byte 5633, and upto 128 bytes of MAC frame 5634. Data frame 5630 conforms to the Zigbeephysical layer specification and can be used to communicate informationbetween devices in lighting system 5410. Data frame 5630 is sentaccording to the timing illustrated in FIG. 55 four bytes at a time ineach gap 5521 until the entire data frame 5630 has been transmitted.

Preamble 5631 comprises four bytes of alternating ones and zeros thatthe receivers in all devices detect and adjust receiver parameters, suchas gain, accordingly. The start byte 5632 is a unique code that allreceivers detect and synchronize byte boundary timing to. The lengthbyte 5633 identifies the length of the MAC frame 5634 in bytes. MACframe 5634 contains data as defined by the Zigbee MAC layerspecification.

FIG. 56 is one of many possible physical layer data frame 5630 formats.The preamble 5631, start 5632, and length 5633 could be completelydifferent and still remain compatible with the Zigbee MAC layerspecification provided that MAC frame 5634 is properly communicated fromthe MAC layer of a transmitting device to the MAC layer of receivingdevices. To support different higher layer protocols even MAC frame 5634could be completely different. Preamble 5631 may or may not be necessarywith any MAC layer protocol depending on the capabilities of the receivecircuitry.

FIG. 57 is an example block diagram for an illumination device 5411 thatcomprises power supply 5741, controller IC 5742, and LED chain 5743. LEDchain 5743 preferentially comprises red LEDs 5754 connected in serieswith resistors 5755 connected in parallel with each red LED 5754.Typically, an illumination device 5411 would comprise additional chainsof white LEDs for instance, but such chains are not shown forsimplicity. As such, FIG. 57 as drawn is a block diagram for anillumination device 5411 that produces red light for instance.

Power supply 5741 accepts the AC mains 5413 and produces DC voltage 5744that provides power for controller IC 5742 and LED chain 5743. Themagnitude of DC voltage 5744 depends on the number of LEDs 5754 in LEDchain 5743. Power supply 5741 also produces synchronization signal 5745for controller IC 5742 to synchronize to. Signal 5745 preferentially isa low voltage version of the AC mains 5413 voltage that PLL and timingcircuitry 5748 can accept and phase lock to.

Controller IC 5742 comprises PLL and timing circuitry 5748, controlcircuitry 5749, PLI (physical layer interface) 5750, receiver 5751, PWM5752, mux 5753, and current source 5756. PLL and timing circuitry 5748locks to the AC mains 5413 frequency and phase and produces the timingillustrated in FIG. 55. During PWM time 5520, mux 5753 enables PWM 5752to control current source 5756, which can cause LED chain 5743 toproduce illumination depending on the state of the PWM 5752 output.During gap time 5521, mux 5753 enables PLI 5750 to control currentsource 5756. When transmitting data 5522, PLI 5750 modulates currentsource 5756 with preferentially scrambled non return to zero (NRZ) data,and when not transmitting data 5522, PLI 5750 disables current source5756.

Receiver 5751 monitors LED chain 5743 during gap times 5521 when PLI5750 is not transmitting data and forwards recovered data if present toPLI 5750. PLI 5750 interfaces to control circuitry 5749, whichimplements the MAC layer protocol and higher layers used forillumination devices 5411 to communicate properly. When transmitting,PLI 5750 accept MAC frames 5634 from control circuitry 5749, generatespreambles 5631, start bytes 5632, and length bytes 5633, scrambles thelength bytes 5633 and MAC frames 5634 with well known techniques, andforwards the resulting data to current source 5756. Likewise whenreceiving, PLI 5750 accepts serial received data from receiver 5751,unscrambles the length bytes 5633 and MAC frames 5634, removes preambles5631, start bytes 5632, and length bytes 5633, and forwards MAC frames5634 to control circuitry 5749.

FIG. 57 is just one example of many possible illumination device 5411block diagrams. For instance, preferentially illumination devices 5411should comprise additional chains of different color LEDs such as white,or green and blue to produce white light. FIG. 57 does not show suchchains for simplicity. Such additional chains would be enabled duringPWM times 5520 and disabled during gap times 5521 when receiving data.When transmitting data, such additional chains would preferentially bemodulated with the same data as LED chain 5743.

Additionally, receiver 5751 could be connected to a silicon photodiodeor other optical sensing device for receiving data. FIG. 57preferentially illustrates LED chain 5743 sensing received light sincesuch LEDs are used to produce illumination as well. PWM 5752 can beremoved if illumination device 5411 does not need to be dimmable.Control circuitry 5749 could reside somewhere else, for instance in anexternal microcontroller. Controller IC 5742 functionality could beimplemented with various electronic components instead of a completelyintegrated solution.

FIG. 58 is one of many possible block diagrams for receiver 5751 thatcomprises switch 5860, amplifier 5861, low pass filter 5862, ADC 5863,and DSP 5864, and that interfaces with LED chain 5743. Light modulatedwith data and incident on LEDs 5754 induce current in each LED 5754 thatflows in a loop through each resistor 5755. The voltages consequentlyinduced across each resistor 5755 substantially sums to produce a largervoltage across signals 5744 and 5747, which is then further gained byamplifier 5861. Low pass filter 5862 substantially eliminates any noiseor interference near and above the A/D Clock 5867 frequency that couldalias into the signal bandwidth.

ADC 5863 preferentially has an over-sampling delta sigma architecturethat samples the analog input at a high frequency, which is 9.44 MHz inthis example, and low resolution, and then digitally low pass filtersthe result to produce high resolution samples at a substantially lowerfrequency, which is 7.68 kHz in this example. The high resolution ADC5863 output preferentially is further processed by DSP 5864 to increasechannel bandwidth using well known decision feedback equalizationtechniques.

Switch 5860 is turned on when CLR 5865 goes low momentarily at thebeginning of each gap period 5521 to short signals 5744 and 5747together just prior to receiving data, which produces a low frequencyaffect on the received signal. DSP 5864 eliminates this and other lowfrequency affects such as from ambient light and 60 Hz interference, bypreferentially monitoring and storing ADC 5863 output samples when nodata is being received and subtracting average values of such samplesfrom ADC 5863 results when receiving data. DSP 5864 alternatively couldimplement a high pass filter to remove such affects.

FIG. 58 is just one of many possible block diagrams for receiver 5751,which could receive data using a silicon photodiode instead of LED chain5743. Amplifier 5861 could be configured as a trans-impedance amplifierto detect current instead of voltage from LED chain 5743. The ADC 5863architecture could be well known FLASH or SAR or could be completelyeliminated depending on the quality of the amplifier 5861 output.Likewise, DSP 5864 may or may not be needed depending on performance.Additionally, a variety of different channel equalization techniquescould be implemented instead of decision feedback. As such FIG. 58 isjust an example.

FIG. 59 is an example block diagram for PLL and timing circuitry 5748that comprises comparator 5970, PLL 5971, dividers 5972 and 5973, anddivider/decode 5974 and that produces the clocks synchronized to the ACmains 5413 used for controller IC 5442 to operate. Signal 5745 frompower supply 5741 is converted to AC mains clock 5975 with a frequencyand phase equal to the AC mains 5413 by comparator 5970. AC mains 5413frequency is assumed to be 60 Hz in this example. AC mains clock 5975frequency is multiplied by 1,572,864 by PLL 5971 to produce the A/DClock 5867 with a frequency approximately equal to 9.44 MHz. A/D Clock5867 is divided by 12288 by divider 5972 to produce bit clock 5866 witha frequency equal to 7.68 kHz, which is also precisely equal to theinstantaneous bit rate of bytes 5522. Divider 5973 divides bit clock5866 by 32 and also produces the pulsed signal CLR 5865. The output ofdivider 5973 is further divided by four and decoded by divider/decode5974 to produce channel clocks 5524.

FIG. 59 illustrates one of many possible PLL and timing circuitry 5748block diagrams that synchronizes the timing of controller IC 5742 to theAC mains 5413 frequency and phase. Depending on the architecture ofcontroller IC 5742 as described previously PLL and timing circuitry 5748could be completely different. For example, PLL 5971 could lock directlyto the AC mains 5413 without comparator 5970.

FIG. 60 is an example diagram illustrating the timing of data beingreceived at the beginning of a gap 5521 on channel one (1) 5524. In thisexample, the gap 5521 period is one bit clock 5866 longer than the totalnumber of bits to be communicated within such gap 5521. The gap 5521time starts at time 6080 when bit clock 5866 and CLR 5865 go high. Alsoat time 6080 mux 5753 switches control of current source 5756 to PLI5750, which is configured to receive data in this example andconsequently ensures that current source 5756 is disabled. Data bytes5522 can begin to be communicated one bit at a time starting at time6081 when AC mains clock 5413 and channel one 5524 clock go high.

Traces 6082 and 6083 represent the voltages on Vled 5747, which is thebottom of LED chain 5743, when received data is not present (Vled 5747Ambient) and is present (Vled 5747 Receiving) respectively. When CLR5865 is high, Vled 5747 is shorted to the power supply 5744. Just priorto CLR 5865 going high, current source 5756 may be enabled or disabledso the voltage on Vled 5747 is unknown. After CLR 5865 goes low ambientlight induces a voltage across LED chain 5743, which causes traces 6082and 6083 to drop exponentially. As shown on trace 6082, if no data isbeing received, the voltage on Vled 5747 may settle after many bit clock5866 periods and could cause data errors when receiving data as shown ontrace 6083. Consequently, DSP 5864 preferentially subtracts an averagedversion of trace 6082 from Vled 5747 during gap 5521 times when data isbeing received.

Since illumination devices 5411 are synchronized to the same AC mains5413 signal, the bit clocks 5866 in all such devices are alsosynchronized in both frequency and phase. Trace 6083 illustrates thevoltage on Vled 5747 in a receiving illumination device 5411 when asecond illumination device 5411 is sending the sequence beginning withone, zero, and one during the three bit clock 5866 periods after time6081. A one in this example is represented by light being on whichproduces a lower voltage on Vled 5747 relative to power supply 5744. ADC5863 samples Vled 5747 when bit clock 5866 goes high, which is preciselyat the times 6084, 6085, and 6086 when Vled 5747 has the largest signal.If illumination devices 5411 were not synchronized to each other throughthe AC mains 5413 or other means, receiver 5751 in a receivingillumination device 5411 would need to recover a clock from the receivedsignal Vled 5747 prior to recovering data, which would substantiallyincrease the complexity of receiver 5751 and potentially degradeperformance.

FIG. 60 is just one example of many possible timing diagrams. Forinstance, if receiver 5751 was connected to a dedicated siliconphotodiode, CLR 5865 and switch 5860 would not be needed. Likewise, thegap 5521 period could have started at time 6081 instead of 6080 with orwithout a dedicated silicon photodiode. Depending on the data rate andsensitivity required for the application, traces 6082 and 6083 could becompletely different. As such FIG. 60 is just one example.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

Seventh Embodiment

Systems and methods are also disclosed for light sources that use thephoto-sensitivity of one or more colored LEDs to determine at least aportion of the emission spectrum of a white light source or other broadspectrum light emitter. As described herein, the white LED or otherbroad spectrum light emitter can be used as the light source, ifdesired, and the same one or more colored LEDs or different LEDs, ifdesired, can be used to emit light and to adjust a color point producedby the light source. Applications for the disclosed embodiments includebut are not limited to general lighting, LCD backlighting, projectors,and direct emission displays such as OLEDs and digital billboards.Various embodiments are described with respect to the drawings below.Other features and variations can also be implemented, if desired, andrelated systems and methods can be utilized, as well.

One embodiment includes a method and system to set a precise colortemperature produced by a substantially white light source, such as aphosphor coated blue LED, or some other broad spectrum light emitter, incombination with one or more colored or substantially mono-chromaticLEDs during the manufacturing of a device, such as an LED lamp, adisplay backlight, a projector, a digital billboard, or AMOLED (ActiveMatrix OLED) display, and to maintain such color temperature over theoperating life of such a device. The method involves analyzing a portionof the spectrum of the white light source or broad spectrum lightemitter using one or more colored LEDs as wavelength selective lightsensors and then using such colored LEDs (or one or more additionaldifferent LEDs if desired) to emit light whereby adjusting the color oflight produced by the combination of the white light source and thecolored LEDs. These LEDs allow for the color point of the light sourceto be adjusted, as desired, based upon the measurements made withrespect to portions of the spectrum of the broad spectrum light emitter.Embodiments further include a light source comprising a white lightsource and colored LEDs, which could be a pixel in a digital billboardor AMOLED, or the entire light source for a lamp, backlight, orprojector, for instance.

The disclosed embodiments apply to any broad spectrum light emitterand/or substantially white light source and any number of colored LEDs.Of particular interest, however, and as described in more detail below,is the combination of red, green, blue, and white LEDs. In such exampleillustration, the red, green, and blue LEDs analyze the spectrum oflight produced by the white LED by each LED operating as a differentwavelength selective light detector. The blue LED measures the blue partof the spectrum, the green LED measures the green plus blue parts of thespectrum, and the red LED measures substantially the entire spectrumwith emphasis on the red and green portions, of the white LED lightsource. Subsequent to such spectral analysis, the red, green, and blueLEDs emit light with intensities adjusted to produce a desired colorpoint when combined with light produced by the white LED.

To reduce optical measurement errors due in particular to variations inLED responsiveness to incident light, further embodiments create ratiosof signals induced on each LED by the white LED and other LEDs that areused to determine relative brightness of each LED to produce the desiredcolor point. For instance and as described in one example herein, thebrightness of the spectrum of the white LED filtered by the red, green,and blue LEDs is determined relative to the brightness of the blue LED.Additionally, the brightness of the green and red LEDs are determinedrelative to the brightness of the blue LED. All such relative brightnesslevels can then be compared to the desired relative brightness levelsbetween the red, green, and blue LEDs and the three different spectralbands produced by the white. LED, and the brightness of the red, green,and blue LEDs, and can be adjusted to produce the desired color pointfrom all four LEDs.

Methods for using measured ratios of light are disclosed herein and alsowith respect to additional embodiments described herein, for example,with respect to the third embodiment. The disclosed embodiments includespectral analysis of a substantially white light to compensate forspectral variations in the emissions of such white light source. Themethods described herein are associated with measuring ratios of emittedlight, further comparing such ratios to desired ratios, and furtheradjusting the brightness produced by the LEDs in response to suchratios.

Specifically related to phosphor coated white LEDs, another aspect ofthe disclosed embodiments compensate for common variations between whiteLEDs during manufacturing and variations that occur over time in aparticular LED. The amount of blue light produced by the blue LED thatdoes not get absorbed by the phosphor relative to the amount of lightemitted by the phosphor varies with phosphor thickness and uniformityduring manufacturing and with phosphor degradation over time. With themethods described herein, the amount of blue light relative to theamount of phosphor converted light produced by the white LED can bedetermined and the amount of light produced by associated red, green,and blue LEDs or just red and green LEDs for instance can be adjusted tocompensate for the difference in such ratio from a desired ratio.

The calibration methods and apparatus described herein address issuesfor devices using groups of different colored LEDs directly or asbacklights for illumination. Such calibration methods reduce the needfor specially binned LEDs for the production of lamps, displays, orbacklights, and maintain the color or color temperature of the lightproduced over the operating life of the device.

As stated above, this seventh embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to this embodiment can beused within the other described embodiments, as desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to calibration and detection systems and methodsdescribed in this seventh embodiment, as desired. Further, as statedabove, the structures, techniques, systems and methods described withrespect to this seventh embodiment can be used in the other embodimentsdescribed herein, and can be used in any desired lighting relatedapplication, including liquid crystal displays (LCDs), LCD backlights,digital billboards, organic LED displays, AMOLED (Active Matrix OLED)displays, LED lamps, lighting systems, lights within conventional socketconnections, projection systems, portable projectors and/or otherdisplay, light or lighting related applications.

Turning now to the drawings, FIG. 61 is an example block diagram forlight source 6110 that uses a broad spectrum light emitter andmulti-colored LEDs to produce a fixed blended color emitted by suchlight source. In this example, such broad spectrum light emitters arewhite LEDs 6124 and 6128 and the multi-colored LEDs are red LEDs 6121and 6125, green LEDs 6122 and 6126, and blue LEDs 6123 and 6127,however, any type of emitter that produces substantially white light andany combination of different colored LEDs can be used. Such light source6110 can be used in any application including but not limited to generallighting, LCD backlighting, projectors, and direct emission displayssuch as OLEDs and digital billboards. As such, a broad spectrum lightemitter as used herein is generally meant to include any light emitterthat includes one or more light sources that alone or together emit aspectrum of light across multiple color regions, such as two or moredifferent colored light sources and/or a white light source. Forexample, a white LED that operates to produce white light would be abroad spectrum light emitter as used herein. As another example, a blueLED and a green LED that operate together to produce mixed blue/greenlight would also be a broad spectrum light emitter as used herein. Othercombinations of different colored LEDs could also be used tosimultaneously produce light across multiple color regions so as tooperate as a broad spectrum light emitter. In short, a broad spectrumlight emitter is one that simultaneously produces or emits light inmultiple color regions.

In this example FIG. 61, light source 6110 comprises controller 6111 andRGBW (red, green, blue, white) LED packages 6112 and 6113. LED package6112 comprises red LED 6121, green LED 6122, blue LED 6123, and whiteLED 6124. LED package 6113 comprises red LED 6125, green LED 6126, blueLED 6127, and white LED 6128. Such red, green, blue, and white LEDs arenot necessarily combined in RGBW LED packages 6112 and 6113, however,since such packages are commonly available, for some applications suchpackages may be preferred.

Controller 6111 comprises eight output drivers 6118, control circuitry6116, and current sense 6117 in this example FIG. 61. Each output driver6118 comprises a current source 6120 and modulator 6119 that control thecurrent to each LED 6121 through 6128 and optionally the duty cycle ofsuch current to control the intensity of light produced by each such LED6121 through 6128. Current sense 6117 can measure the photo-currentinduced in red LEDs 6121 and 6125, green LEDs 6122 and 6126, and blueLEDs 6123 and 6127 by the other LEDs 6121 through 6128 as described inFIGS. 66A-D, 67A-D, 68A-D and 69-A-D. The anodes of LEDs 6121 through6128 are shown to be tied together and to the power supply Vd 6114. Thecathodes of LEDs 6121 through 6128 are shown connected to signal busVC[7:0]6115, which connects each cathode to a different output driver6118 and current sense 6117 input in controller 6111.

FIG. 61 is just one example of many possible block diagrams for lightsource 6110. For instance, any broad spectrum emitter in combinationwith any combination of different colored LEDs can be used. A broadspectrum emitter is generally meant to include an emitter that emits aspectrum of light across multiple color regions, such as a white lightsource. Additionally, any number of broad spectrum emitters and LEDs canbe combined to produce light source 6110 with any emission power. Whenthe broad spectrum light source is a white LED, any number of such whiteand colored LEDs can be connected in series or parallel, with any numberof driver circuits. Controller 6111 can comprise a single or manyintegrated circuits and discreet components. Driver 6118 may or may notcomprise modulator 6119, in which case, current sources 6120 would beadjusted to vary the intensity of light produced by each attached LED.Likewise, current sense 6117 could measure voltage instead of current orsome combination of both. As such FIG. 61 is simply an example blockdiagram for light source 6110.

FIG. 62 is an example block diagram for current sense 6117, whichcomprises ADC (analog to digital converter) 6232, resistor (R) 6231, andmultiplexer (mux) 6230. As shown in both FIG. 61 and FIG. 62, the inputsto current sense 6117 comprise Vd 6114, which is connected to the anodesof LEDs 6121 through 6128 in this example, and VC[7:0]6115 signals thatare connected to the cathodes of each LED 6121 through 6128. The outputof ADC 6232 is forwarded to control circuitry 6116, which processes theinformation and controls drivers 6118. To measure the photocurrentinduced on any LED 6121 through 6128, multiplexer 6230 passes theselected signal from VC[7:0]6115 from the cathode of the selected LED toresistor 6231 and ADC 6232. Since Vd 6114 is connected to the oppositeside of resistor 6231 and to the anode of the selected LED, any currentinduced in the selected LED passes through resistor 6231 and induces asmall voltage, which is measured by ADC 6232. Preferably, the resistanceof resistor 6231 should be selected to never produce a sufficiently highvoltage when measuring photocurrent to forward bias the LED. Forinstance, a typical resistor value of 100 k ohms would produce a typicalADC 6231 input voltage of 10-100 mV.

FIG. 62 is just one example of many possible block diagrams for currentsense 6117. For example, if resistor 6231 is removed, ADC 6232 couldmeasure the open circuit voltage induced across each LED 6121 through6128. Multiplexer 6230 is shown to select between all 8 LEDs, however,white LEDs 6124 and 6128 are typically not measured and consequently donot need to be connected to current sense 6117. Multiplexer 6230 is notneeded at all if an ADC 6232 is connected directly to each LED cathode.As such, FIG. 62 is just one example of many possible current sense 6117block diagrams.

FIG. 63 is an illustration of exemplary emission spectra produced byred, green, blue, and white LEDs 6121 through 6128 in light source 6110.Emission spectrum 6340 illustrates one possible spectrum emitted bywhite LEDs 6124 and 6128. Since white LEDs typically comprise blue LEDswith a phosphor coating, the emission spectrum 6340 shows a peak around450 nm, which is produced by the blue LED, and a much broader peakaround 550 nm, which is produced by the phosphor. The blended spectrumappears as white light, however, the color or color temperature of suchwhite light can vary substantially.

Emission spectrums 6341 (blue), 6342 (green), and 6343 (red) representtypical spectrums produced by blue LEDs 6123 and 6127, green LEDs 6122and 6126, and red LEDs 6121 and 6125 respectively. Typical peak emissionwavelengths are 450 nm for blue, 530 nm for green, and 625 nm for red,which are represented by the highest intensity points in emissionspectra 6341 (blue), 6342 (green), and 6343 (red) respectively. The peakemission wavelength for green LEDs 6122 and 6126 typically is justshorter than the peak emission wavelength produced by the phosphor inwhite LEDs 6124 and 6128, while the peak emission wavelength for redLEDs 6121 and 6125 typically is longer than most of the optical powerproduced by white LEDs 6124 and 6128.

FIG. 63 is one example of many possible emission spectrums from theindividual lighting elements in light source 6110. For instance, lightsource 6110 can have a broad spectrum emitter to typically produce whitelight that is not an LED. In such case, the emission spectrum typicallywould be substantially different from emission spectrum 6340. Likewise,light source 6110 may comprise more or less colored LEDs and such LEDscould be any color. As such the LEDs in light source 6110 could havemore or less emission spectrums than spectrums 6341, 6342, and 6343shown in FIG. 63, and each spectrum could have substantially differentpeak emission wavelengths and other spectral characteristics. FIG. 63 isjust one example of many possible spectral plots.

FIG. 64 is illustrates two example emission spectrums from a white LED6124 or 6128 that produce two different white color temperatures. Inthis example both emission spectrums are produced by a white LED 6124 or6128 comprising of a phosphor converted blue LED. Such phosphor could bein contact with such blue LED or separated by some distance. Thedifference in the two spectrums could be produced by different phosphorthickness for two different LEDs at the end of a manufacturing line orcould be produced by the same LED at two different times or at twodifferent temperatures. LED phosphor coatings are well known to changecharacteristics over temperature and to degrade over time. Likewise, theoptical power emitted by the blue LED in white LED 6124 or 6128 is alsowell known to change over operating conditions and lifetime. FIG. 64 isjust one example of many possible differences in spectral emissions fromtwo white LEDs or the same LED under different conditions.

FIG. 64 illustrates the spectral peak 6446 produced by such blue LED inwhite LED 6124 or 6128, and substantially broader spectral peaks 6444and 6445 produced by such phosphors in white LED 6124 or 6128. In thisexample FIG. 64, spectral peak 6444 could represent the emissionsproduce by such phosphor in white LED 6124 or 6128 at the time it wasmanufactured, and lower spectral peak 6445 could represent the emissionsproduced by such phosphor in white LED 6124 or 6128 after some time. Assuch, the white color temperature of the light produced by white LED6124 or 6128 is shown to change over time in this example.

FIG. 65 is one example of the spectral responsiveness 6552 (red), 6551(green), and 6550 (blue) of the red 6121 and 6125, green 6122 and 6126,and blue 6123 and 6127 LEDs in light source 6110 respectively. Spectralresponsiveness is the relative amount of current induced on an LED by afixed incident optical power as function of incident wavelength. Asshown in this example FIG. 65, spectral responsiveness 6550 (blue), 6551(green), and 6552 (red) illustrates that blue 6123 and 6127, green 6122and 6126, and red 6121 and 6125 LEDs produce current in response tolight with incident wavelengths roughly equal to or shorter than suchblue, green, and red LED peak emission wavelengths as shown in emissionsspectrums 6341 (blue), 6342 (green), and 6343 (red). As such, such redLEDs can detect light from such red, green, and blue LEDs, such greenLEDs can detect light from such green and blue LEDs, and such blue LEDscan detect light from such blue LEDs. Likewise, such red, green, andblue LEDs can detect light from different parts or portions of aspectrum emitted by a broad spectrum light emitter as filtered by theseLEDs, such as, for example, filtered portions of the spectrum 6340 fromwhite LED 6124 or 6128 as shown in FIG. 63.

Since light source 6110 may comprise a different number of differentcolored LEDs, FIG. 65 illustrates the spectral responsiveness of justone example set of LEDs in light source 6110. Likewise, responsiveness6550 (blue), 6551 (green), and 6552 (red) are just rough approximationsfor the spectral responsiveness of such blue, green, and red LEDsrespectively. Actual responsiveness may vary substantially. As such,FIG. 65 is just one example.

The following equations are associated with FIGS. 66A-D. In particular,equation 24 is associated with FIGS. 66A-B. Equation 25 is associatedwith FIGS. 66C-D. And equation 26 provides a ratio using equations 24and 25.

V_(b1w0)=E_(w0b)R_(b1)C_(b1w0)  [EQ. 24]

V_(b1b0)E_(b0)R_(b1)C_(b1b0)  [EQ. 25]

E _(w0b) /E _(b0)=(V _(b1w0) N _(b1b0))C ₀  [EQ. 26]

FIGS. 66A-D provide an exemplary first step in an exemplary method toset and maintain a precise color temperature produced by a combinationof red, green, blue, and white LEDs 6121 through 6128 in light source6110. In such first step, current induced in blue LED 6127 by white LEDs6124 as shown in FIGS. 66A-B is compared to current induced in blue LED6127 by blue LED 6123 as shown in FIGS. 66C-D. White LED 6124 isilluminated by producing current I_(w0) in a current source 6120, andthe current induced in blue LED 6127 is measured by connecting resistor6231 across LED 6127 and measuring the resulting voltage V_(b1w0) by ADC6232. Equation 24 illustrates that the induced voltage V_(b1w0) is equalto the power emitted by LED 6124 E_(w0b) times the responsiveness R_(b1)of LED 6127 times a constant Cb1w0. Spectral plot 6660 illustrates theresponsiveness 6550 of blue LED 6127 superimposed on the spectrum 6340of white LED 6124 along with the alternative phosphor produced spectrum6445 that could result from white LED 6124 aging. As shown in spectralplot 6660 of FIG. 66B, the resulting current induced in blue LED 6127 bywhite LED 6124 should be independent of variations in the light producedby such phosphor.

Subsequently, blue LED 6123 is illuminated by producing current Ib0 in acurrent source 6120, and the current induced in blue LED 6127 is againmeasured by connecting resistor 6231 across LED 6127 and measuring theresulting voltage. Equation 25 illustrates that the induced voltageVb1b0 is equal to the power emitted by LED 6123 Eb0 times theresponsiveness Rb1 of LED 6127 times a constant Cb1b0. Spectral plot6661 as shown in FIG. 66D illustrates the responsiveness 6550 of blueLED 6127 superimposed on the spectrum 6341 of blue LED 6123. As shown, asignificant portion of the emitted power Eb0 induces current in LED6127.

Equation 26 illustrates the result of dividing equation 24 by equation25 and combining Cb1w0 and Cb1b0 to produce the constant C0. As shown inequation 26 and spectral plots 6660 and 6661, the ratio of the emittedpowers Ew0b over Eb0 with wavelengths roughly shorter than 450 nm inthis example is proportional to the ratios of the induced voltages Vb1w0over Vb1b0. The responsiveness of blue LED 6127 cancels out.

The following equations are associated with FIGS. 67A-D. In particular,equation 27 is associated with FIGS. 67A-B. Equation 28 is associatedwith FIGS. 67C-D. And equation 29 provides a ratio using equations 27and 28.

V_(g0w0)=E_(w0g)R_(g0)C_(g0w0)  [EQ. 27]

V_(g0b0)=E_(b0)C_(g0b0)  [EQ. 28]

E _(w0g) /E _(b0)=(V _(g0w0) /V _(g0b0))C ₁  [EQ. 29]

FIGS. 67A-D provide an exemplary second step in an exemplary method toset and maintain a precise color temperature produced by a combinationof red, green, blue, and white LEDs 6121 through 6128. Such second stepis identical to such first step illustrated in FIGS. 66A-D except thatgreen LED 6122 is used to measure the light produced by white 6124 andblue 6123 LEDs. White 6124 and blue 6123 LEDs are again illuminated byproducing currents Iw0 and Ib0 respectively in current sources 6120respectively as shown in FIGS. 67A-B and 67C-D. The resulting voltagesVg0w0 and Vg0b0 induced by white 6124 and blue 6123 LEDs respectively ongreen LED 6122 are equal to the white LED 6124 emitted power Ew0g andthe blue LED 6123 emitted power Eb0 times the green LED 6122responsiveness times the constants as shown in equations 27 and 28.Equation 29 illustrates the result of dividing equation 27 by equation28 which shows the ratio of the emitted powers Ew0g over Eb0 withwavelengths roughly shorter than 550 nm in this example is proportionalto the ratios of the induced voltages Vg0w0 over Vg0b0. Theresponsiveness of green LED 6122 cancels out. Spectral plot 6770 asshown in FIG. 67B illustrates that light from the blue peak and some ofthe light from the phosphor converted peak induce current in green LED6122, while spectral plot 6771 as shown in FIG. 67D illustrates that allthe light from blue LED 6123 induces current in green LED 6122.

The following equations are associated with FIGS. 68A-F. In particular,equation 30 is associated with FIGS. 68A-B. Equation 31 is associatedwith FIGS. 67C-D. Equation 32 is associated with FIGS. 68E-F. Andequations 33 and 34 provide ratios using equations 30, 31 and 32.

V_(r0w0)=E_(w0r)R_(r0)C_(r0w0)  [EQ. 30]

V_(r0b0)=E_(b0)R_(r0)L_(0b0)  [EQ. 31]

V_(r0g0)=E_(g0)R_(r0) C_(r0g0)  [EQ. 32]

E _(w0r) /E _(b0)=(V _(r0w0) /V _(r0b0))C ₂  [EQ. 33]

E _(g0) /E _(b0)=(V _(r0g0) /V _(r0b0))C ₃  [EQ. 34]

FIGS. 68A-F illustrate an exemplary third step in an exemplary method toset and maintain a precise color temperature produced by a combinationof red, green, blue, and white LEDs 6121 through 6128. While the firststep illustrated in FIGS. 66A-D determined the ratio of light producedby white LED 6124 over blue LED 6123 as filtered by blue LED 6127 andthe second step illustrated in FIGS. 67A-D determined the ratio of lightproduced by the white LED 6124 over the blue LED 6123 as filtered bygreen LED 6122, the third step determines the ratio of light produced bywhite LED 6124 over blue LED 6123 as filtered by red LED 6121.Additionally in the third step, the ratio of light produced by green LED6122 over blue LED 6123 is also determined by red LED 6121. White 6124,blue 6123, and green 6122 LEDs are illuminated by current sources 6120producing currents Iw0, Ib0, and Ig0 as shown in FIGS. 68A, 68C and 68E,respectively. The voltages induced across red LED 6121 by white 6124,blue 6123, and green 6122 LEDs are Vr0w0, Vr0b0, and Vr0g0 respectively.Equations 30, 31, and 33 illustrate that such induced voltages Vr0w0,Vr0b0, and Vr0g0 are equal to the optical powers Ew0r, Eb0, and Eg0produced by the white 6124, blue 6123, and green 6122 LEDs respectivelytimes the responsiveness of red LED 6121 times constants. Equations 33and 34 illustrate the division of equations 30 and 32 by equation 31respectively and show that the ratio of optical power emitted by thewhite LED 6124 over the blue LED 6123 as filtered by the red LED 6121 isproportional to the ratio of Vr0w0 over Vr0b0, and that the ratio ofoptical power emitted by the green LED 6122 over the blue LED 6123 asfiltered by the red LED 6121 is proportional to the ratio of Vr0g0 overVr0b0.

Spectral plot 6880 shown in FIG. 68B illustrates that red LED 6121 isresponsive to nearly the complete emission spectrum of white LED 24including nearly the complete spectral emission peak due to phosphorconversion, which means any change or degradation in phosphor efficiencywill affect the current induced in red LED 6121 by white LED 6124.Spectral plot 6881 shown in FIG. 68D and spectral plot 6882 shown inFIG. 68F illustrate that red LED 6121 is also responsive tosubstantially the complete spectral emissions from blue 6123 and green6122 LEDs, however, the responsiveness of red LED 6121 to blue LED 6123is reduced.

The following equations are associated with FIGS. 69A-D. In particular,equation 35 is associated with FIGS. 69A-B. Equation 36 is associatedwith FIGS. 69C-D. And equation 37 provides a ratio using equations 35and 36.

V_(r1g0)=E_(g0)R_(r1)C_(r1g0)  [EQ. 35]

V_(r1r0)=E_(r0)R_(r1)C_(r1r0)  [EQ. 36]

E _(g0) /E _(r0)=(V _(r1g0) /V _(r1r0))C ₄  [EQ. 37]

The fourth exemplary step in the exemplary method to set and maintain aprecise color temperature produced by a combination of red, green, blue,and white LEDs 6121 through 6128, is illustrated in FIGS. 9A-D in whichthe ratio of currents induced in red LED 6125 by green LED 6122 over redLED 6121 is determined. Current sources 6120 illuminate green 6122 andred 6121 LEDs by producing currents Ig0 and Ir0 respectively, whichinduce voltages Vr1g0 and Vr1r0 respectively across red LED 6125, asshown in FIGS. 69A and 69C. Equations 35 and 36 illustrate that thevoltages Vr1g0 and Vr1r0 are proportional to the green LED 6122 emittedpower Eg0 and the red LED 6121 emitted power Er0 times theresponsiveness of red LED 6125 Rr1 respectively. Equation 37 illustratesequation 35 divided by 36, which shows the ratio of Eg0 over Er0 to beproportional to the ratio of induced voltages Vr1g0 over Vr1g0. Theresponsiveness of red LED 6125 cancels out.

The following equations described with respect to FIGS. 66A-D, 67A-D,68A-F and 69A-D can be used to represent how color matching can beachieved.

E _(w0b) /E _(b0)=(V _(b1w0) /V _(b1b0))C ₀  [EQ. 26]

E _(w0g) /E _(b0) =V _(g0w0) N _(g0b0))C ₁  [EQ. 29]

E _(w0r) /E _(b0)=(V _(r0w0) N _(r0b0))C ₂  [EQ. 33]

E _(g0) /E _(b0)=(V _(r0g0) N _(r0b0))C ₃  [EQ. 34]

E _(g0) /E _(r0)=(V _(r1g0) N _(r1r0))C ₄  [EQ. 37]

E _(r0) /E _(r0)=(V _(r0g0) /V _(r0b0))(V _(r1r0) /V _(r1g0))(C ₃ /C₄)  [EQ. 38]

E _(w0b) /E _(w0r)=(V _(b1w0) /V _(b1b0))(V _(r0b0) /V _(r0w0))(C ₀ /C₂)  [EQ. 39]

E _(w0g) /E _(w0r)=(V _(g0w0) N _(g0b0))(V _(r0b0) /V _(r0w0))(C ₁ /C₂)  [EQ. 40]

In particular, equations 26, 29, 33, 34 and 37 that were described withrespect to FIGS. 66A-D, 67A-D, 68A-F and 69A-D can be used to generateequations 38, 39 and 40. These equations provide an exemplary set ofequations describing the exemplary method to set and maintain a precisecolor emitted by red, green, blue, and white LEDs. Equations 26, 29, 33,and 34 relate the optical power emitted by blue LED 6123 to the opticalpower emitted by white LED 6124 as filtered by blue 6127, green 6122,and red 6121 LEDs and by green LED 6122 respectively. Equation 38divides equation 34 by equation 37 to relate the optical power emittedby blue LED 6123 to the optical power emitted by red LED 6121. Equations26, 29, 33, 34, and 38 relate the emitted power of red 6121, green 6122,and three different filtered versions of white LED 6124 to the emittedpower of blue LED 6123. Such ratios of optical power can be compared todesired ratios as described herein, for example, as described withrespect to the third embodiment, and enable a precise color temperaturelight to be set and maintained by the combination of such red, green,blue, and white LEDs illustrated in this example. Switching LEDs 6121through 6124 with LEDs 6125 through 6128 and repeating the stepsillustrated in FIGS. 66A-D, 67A-D, 68A-F and 69A-D provides the ratiosof optical power emitted by LEDs 6125 through 6128 to balance the colorproduced by all the LEDs in light source 6110 illustrated in thisexample light source and calibration method.

Equation 39 illustrates the ratio of equation 26 over equation 33, whichshows the ratio of light produced by white LED 6124 over the spectrumdetectable by blue LED 6127 divided by the light produced by white LED6124 over the spectrum detectable by red LED 6121. Likewise, equation 40illustrates the ratio of equation 29 over equation 33, which shows theratio of light produced by white LED 6124 over the spectrum detectableby green LED 6122 divided by the light produced by white LED 6124 overthe spectrum detectable by red LED 6121. Such ratios illustrated byequations 39 and 40 can also be compared to desired ratios as describedherein, for example, as described with respect to the third embodiment,and the intensities of the red, green, and blue LEDs can be adjustedrelative to the white LEDs to compensate for changes in the spectrum ofthe white LEDs at the end of a manufacturing line, and over operationconditions and lifetime.

FIG. 70 illustrates the well known CIE 1931 Color Space diagram 7010 forthe XY color space. The range of theoretically producible colors liewithin the boundary 7011, and the range of actual colors producible by acombination of red, green, blue, and white LEDs 6121 through 6128 liewithin the triangle 7012. In this example, the color points produced thered, green, and blue LEDs independently are the corners of the trianglelabeled 7013, 7014, and 7015 respectively. In this example, the desiredcolor point produced by the combination of the red, green, blue, andwhite LEDs 6121 through 6128 is identified as 7016, while in thisexample the actual color point at the time of calibration is identifiedat 7017.

Such difference in color points 7016 and 7017 represents the change thatcan occur as a phosphor based white LED ages for instance. As thephosphor degrades and converts less blue light to other wavelengths,such phosphor converted peak 6444 changes to peak 6445 from FIG. 64relative to blue peak 6446 and the color point shifts from 7016 to 7017as an example. Equation 39 then provides the actual ratio of the opticalpower in blue peak 6446 over approximately the optical power in phosphorconverted peak 6445 at the time of calibration. Equation 39 alsoprovides the desired ratio of the optical power in the blue peak 6446over the same approximation of the optical power in phosphor convertedpeak 6444 at the time the device was manufactured. The ratio of suchactual ratio divided by such desired ratio specifies how much relativeoptical power has shifted from the phosphor converted range of the whiteLED spectrum to the blue LED range of the white LED spectrum. Increasingthe optical power produced by red LEDs 6121 and 6125 and green LEDs 6122and 6126 in the proportion that produces color point 7018 by an amountdetermined by such ratio of such actual ratio over such desired ratioadjusts the color point produced by light source 6110 from the actualcolor 7017 back to the desired color point 7016.

Since typically the responsiveness of red LEDs 6121 and 6125 drops offrapidly with decreasing incident wavelength near typical blue LEDemission wavelength, the current induced in red LEDs 6121 and 6125 bywhite LEDs 6124 and 6128 is dominated by the optical power in thephosphor converted range of a typical white LED. The small amount ofcurrent induced in red LEDs 6121 and 6125 by the blue LED range of thewhite LED spectrum is effectively removed from the calculation resultsby taking the ratio of such actual ratio over such desired ratio.

FIG. 70 and the associated preceding description illustrate just oneexample of how the systems and methods herein can be applied. There aremany other possible applications including but not limited tocalibrating to the color of light source 6110 at the end of amanufacturing line. In such case, such desired ratios can be measuredfrom a control device that produces the desired color point and comparedto the actual ratios measured on production devices. In such case, theactual color point could be in any relation to the desired color pointwith different combinations of additional red, green, and blue LED lightneeded to produce the desired color point. In another example, the colorpoint of the white LED could be deliberately shifted to the green regionof the color diagram with light source 10 comprising such white LEDsalong with only blue and red LEDs. As such, green LEDs would not beneeded since the blue and red LEDs could always measure and adjust thecombined light from the greenish white LEDs, and blue and red LEDs tothe desired color point. Likewise, the substantially white light sourcecould be something other than an LED, in which case differentcombinations of LEDs may be needed. Further, more than three differentcolored LEDs, such red, green, blue, and amber, or red, green, blue,cyan, and magenta, or any other combination of colors could be used toanalyze the spectral emissions of the broadband light source andcompensate for variations to set and maintain a precise color point. Assuch FIGS. 61 through 70 illustrate just one example. Numerousvariations and modifications will become apparent to those skilled inthe art once the above disclosure is fully appreciated.

Eighth Embodiment

It is noted that detailed discussions have been provided above for LEDcalibration systems and methods with respect to the third embodiment andthe seventh embodiment. The following discussion with respect to LEDcalibration systems and methods is also provided as an alternative butrelated discussion of calibration systems and methods. This alternativediscussion is not intended to change or alter the discussions above butis merely included as an additional discussion of possible calibrationtechniques, systems and methods.

LED calibration systems and related methods are disclosed that use thephoto-sensitivity of LEDs to correct for variations between LEDs duringinitial production and over the lifetime of systems using LEDs. Variousembodiments are described with respect to the drawings below. Otherfeatures and variations can also be implemented, if desired, and relatedsystems and methods can be utilized, as well.

In part, the disclosed embodiments relate to groups of LEDs that use thephoto-sensitivity of each other and an optional light source todetermine the light intensity produced by each LED in such group and toadjust such intensity to create and maintain a precise color produced bythe group of LEDs. Applications for the LED calibration systems andmethods include solid state lamps, LCD backlights, and LED displays forinstance. Variations in LED brightness and color should be compensatedfor in order for such devices to have uniform color and brightness. Suchcompensation, which is typically done by measuring the optical outputpower of each individual LED or purchasing specially tested LEDs, isperformed by simply measuring the signal induced on each LED by lightfrom other LEDs in the device or optionally from an additional lightsource.

The disclosed embodiments include a number of methods to set the coloror color temperature produced by a group of LEDs during themanufacturing of a device such as a lamp, an LED display, or an LCDbacklight, and maintaining such color or color temperature over theoperating life of such a device. The methods operate some of the LEDs inphotovoltaic or photoconductive mode to measure the light produced byother LEDs in the group and optionally from a light source, and adjustthe light produced by each LED in such group of LEDs to produce aprecise color or color temperature from such group.

The first method illustrated in FIG. 73A-C relies on the correlationbetween the light produced by an LED from a fixed current and thephotocurrent produced by such LED from a fixed light intensity. Sincesuch correlation is not perfect, such first method is an approximation.However, such first method is the simplest and although not limited tosuch is intended to enable a device with a combination of red, green,and blue LEDs with large intensity variations to self calibraterelatively close to a desired color or color temperature and outputintensity during production and over operating life.

The second method illustrated in FIG. 74A-D uses the same basicmechanisms as the first method to produce a fixed color or colortemperature and output intensity, but uses a light source with typicallya known intensity as a reference and typically requires two LEDs in suchgroup of LEDs to emit light of the same color. Such second methodintroduces an error factor between the light produced by an LED from afixed current and the photocurrent produced from a fixed lightintensity, and mathematically illustrates that such second method isindependent of such error factor and as such is significantly moreaccurate than such first method. Although not limited to such, thesecond method is intended to be used during the manufacturing of adevice to create a precise color or color temperature and overall lightintensity produced by a group of different colored LEDs in a device, butcan also be used over operating life provided a light source isavailable.

The third method illustrated in FIGS. 75A-F, although not limited tosuch, is intended to combine the results of the second method usedduring the manufacturing of a device comprising such group of LEDs withthe first, second, or fourth methods used over the operating life ofsuch device. Initial errors in the correlation between light produced byan LED from a fixed current and the photocurrent produced from a fixedlight intensity are removed. Only changes in such errors over operatinglife introduce affect the color, color temperature, and light intensityproduced by such group of LEDs in a device.

The fourth method illustrated in FIG. 76A-D uses the same basicmechanisms as the first and second methods, but is only capable ofmaintaining the color or color temperature of the light produced by agroup of LEDs. Only the ratios of the emitted intensities can bedetermined so the overall emitted intensity is not precisely controlled.Although not limited to such, the fourth method is intended to be usedover the operating life of such group of LEDs to maintain the color orcolor temperature of the light produced by such device. No externallight source is needed, but typically two. LEDs within the group of LEDsemit the same color light.

The fifth method illustrated in FIG. 79A-C uses the photosensitivity ofan LED as a function of incident wavelength to determine the peakemission wavelength of such LED. A light source produces light with atleast two different wavelengths typically just above and just below theexpected peak emission wavelength range of such LED with the differencein induced photocurrents being directly related to the actual peakemission wavelength of such LED.

Once the relative intensity or both the relative intensity andwavelength of light produced by LEDs within a group of different coloredLEDs are known, the color or color temperature of the combined lightproduced by such group of LEDs can be fixed, adjusted, and maintainedover the operating life of such group of LEDs by adjusting the relativeintensity of light produced by each such LED. A color correction matrixwith coefficients determined by the calibration methods described hereincan provide the compensated intensities to the driver circuitry for eachsuch LED.

The second and fourth methods described in FIGS. 74A-D and 76A-Drespectively typically require two LEDs within such group of LEDs toemit the same color light. For instance, a lamp or LCD backlightcomprising red, green, and blue LEDs would have at least twoindependently controlled red LEDs or serially connected strings of redLEDs. As another example, a lamp with white and red LEDs, would alsohave two independently controlled red LEDs or serially connected stringsof red LEDs. In an LED display or LCD backlight comprising arrays ofpixels of red, green, and blue LEDs, such group of LEDs could comprisetwo red LEDs from two adjacent pixels, for instance. Such two red LEDscould be successively grouped together with each of the remaining twoblue and two green LEDs, for instance, to determine the intensity orrelative intensity produced by all the LEDs in both pixels.Additionally, a uniform light source, such as sunlight, could illuminatesuch arrays of pixels to enable the second method illustrated in FIG.74A-D to produce uniform intensity across the array.

The methods address problems associated with devices using groups ofdifferent colored LEDs directly or as backlights for illumination. Suchcalibration methods reduce the need for specially binned LEDs for theproduction of lamps, displays, or backlights, and maintain the color orcolor temperature of the light produced over the operating life of thedevice.

As stated above, this eighth embodiment can also be used with thetechniques, methods and structures described with respect to the otherembodiments described herein. For example, the calibration and detectionsystems and methods described with respect to this embodiment can beused within the other described embodiments, if desired. Further, thevarious illumination devices, light sources, light detectors, displays,and applications and related systems and methods described herein can beused with respect to calibration and detection systems and methodsdescribed in this eighth embodiment, as desired. Further, as statedabove, the structures, techniques, systems and methods described withrespect to this eighth embodiment can be used in the other embodimentsdescribed herein, and can be used in any desired lighting relatedapplication, including liquid crystal displays (LCDs), LCD backlights,digital billboards, organic LED displays, AMOLED (Active Matrix OLED)displays, LED lamps, lighting systems, lights within conventional socketconnections, projection systems, portable projectors and/or otherdisplay, light or lighting related applications.

Turning now to the drawings, FIG. 71 is an example circuit for measuringthe actual emitted optical power labeled E_(a20) produced by LED 7120,which is driven by constant current source 7121 with the nominal currentof I₀ amps. The actual emitted power is measured by optical power meter7128. The following equation is associated with FIG. 71.

Actual Emitted Power/Nominal Emitted Power=E_(a20) /E _(n20) =E ₂₀  [EQ.41]

Equation 41 relates the actual optical power E_(a20) emitted by LED 7120to the nominal optical power E₂₀ emitted by a group of LEDsrepresentative of LED 7120. The nominal or desired emitted optical powerE_(n) can be any optical power but is typically the average or meanoptical power produced by the group of LEDs representative of LED 7120.The ratio of the actual power emitted by LED 7120 over the nominal poweremitted by the group of LEDs representative of LED 7120 is the result ofequation 41 labeled E₂₀, which is independent of the current produced bycurrent source 7121 and the optical losses between LED 7120 and opticalpower meter 7128 provided such conditions are the same during theoptical power measurements for all LEDs within the group of LEDsrepresentative of LED 7120 and including LED 7120.

The group of LEDs representative of LED 7120 can be a so calledcharacterization lot for the LED 7120 design that is specificallymanufactured to produce LEDs with emission characteristicsrepresentative of the range of emission characteristics anticipatedduring mass production of the LED 7120 design.

FIG. 72 is an example circuit that produces a voltage V_(a30) inducedacross LED 7230 by the nominal optical power E_(n20) described with FIG.71 and emitted by LED 7120. LED 7120 is configured to emit the nominaloptical power E_(n20) as measured by optical power meter 7128 byadjusting the current produced by current source 7121 to an amount I₁.Provided the peak emission wavelength of LED 7230 is roughly equal to orlonger than the peak emission wavelength of LED 7120, the light from LED7120 induces a current in LED 7230 that produces the voltage V_(a30)across resistor 7232 between the anode 7233 and cathode 7234 of LED7230. The following equation is associated with FIG. 72.

Actual Voltage/Nominal Voltage=V_(a30) /V _(n3020) =V ₃₀₂₀ ˜=E _(a30) /E_(n30) =E ₃₀  [EQ. 42]

Equation 42 relates the actual voltage V_(a30) produced by LED 7230 inresponse to the nominal emitted power E_(n20) from LED 7120 to thenominal voltage V_(n3020) produced by a group of LEDs representative ofLED 7230 in response to the nominal emitted power E_(n20). Among otherthings, since variations in the optical path between the LED activeregion and the surface of the LED package approximately equally affectlight entering and leaving the LED and since variations in the quantumefficiency of the active region approximately equally affect theconversion of electric current to light and of light to electricalcurrent, such ratio of voltages is approximately equal to the ratio ofactual optical power E_(a30) emitted by LED 7230 over the nominaloptical power E_(n30) emitted by a group of LEDs representative of LED7230. Such ratio, which is the result of equation 7238 is called E₃₀ forLED 7230.

FIG. 73A-C illustrates a method using the relationship illustrated inFIG. 72 to determine the actual optical power produced by LEDs 7120,7230, and 7340 relative to the nominal optical power produced by groupsof LEDs representative of such LEDs 7120, 7230, and 7340. LEDs 7120,7230, and 7340 could be any combination of colors or could be one color.Two common configurations include red, green, and blue, and red, red,and white for LEDs 7340, 7230, and 7120 respectively. In such method,LED 7120 illuminates both LED 7230 and LED 7340, and then LED 7230illuminates LED 7340. From measurements of induced voltages V_(a30) andV_(a40), the ratio of actual optical power emitted to nominal opticalpower emitted can be calculated for each LED 7120, 7230, and 7340.

The following equations are associated with FIGS. 73A-C. In particular,equations 43A-B are associated with FIG. 73A. Equations 44A-B areassociated with FIG. 73B. Equations 45A-B are associated with FIG. 73C.And equations 46-51 utilize the other equations.

V _(a30)˜=(V _(n3020))(E ₃₀)(E ₂₀)  [EQ. 43A]

V _(a30) /V _(n3020) =V ₃₀₂₀˜=(E ₃₀)(E ₂₀)  [EQ. 43B]

V _(a40)˜=(V _(a4020))(E ₄₀)(E ₂₀)  [EQ. 44A]

V _(a40) /V _(n4020) =V ₄₀₂₀˜=(E ₄₀)(E ₂₀)  [EQ. 44B]

V _(a40)˜=(V _(n4030))(E ₃₀)(E ₄₀)  [EQ. 45A]

V _(a40)/(V _(n4030))=/V ₄₀₃₀˜=(E ₃₀)(E ₄₀)  [EQ. 45B]

Rearranging 43B provides:

E ₂₀˜=(V ₃₀₂₀)(E ₃₀)  [EQ. 46]

Substituting 46 into 44B provides:

V ₄₀₂₀˜=(E ₄₀)(V ₃₀₂₀)(E ₃₀)

E ₃₀˜=(E ₄₀)(V ₃₀₂₀)/(V ₄₀₂₀)  [EQ. 47]

Substituting 47 into 45B provides:

V ₄₀₃₀˜=(E ₄₀)(E ₄₀)(V ₃₀₂₀)/(V ₄₀₂₀)

(V ₄₀₃₀)(V ₄₀₂₀)/(V ₃₀₂₀)˜=(E ₄₀)²  [EQ. 48]

E ₄₀˜=square root [(V ₄₀₃₀)(V ₄₀₂₀)/(V ₃₀₂₀)]  [EQ. 49]

From 45B,

E ₃₀˜=(V ₄₀₃₀)(E ₄₀)  [EQ. 50]

From 44B

E ₂₀˜=(V ₄₀₂₀)/(E ₄₀)  [EQ. 51]

Current source 7121 produces the nominal current I₀, which causes LED7120 to emit optical power E_(a20), which induces voltages V_(a30) andV_(a40) across resistors 7232 and 7342 respectively. Equations 43A-Brelate V_(a30) to the voltage V_(n3020) induced on a group of LEDsrepresentative of LED 7230 by the nominal power emitted an LED 7120 asshown in FIG. 73A. The actual voltage V_(a30) approximately equals thenominal voltage V_(n3020) scaled by the ratios of actual emitted powerover nominal emitted power E₃₀ and E₂₀ for LED 7230 and LED 7120respectively. The parameter V₃₀₂₀ is defined as the ratio of the actualvoltage V_(a30) over the nominal voltage V_(n3020).

Equations 44A-B and 45A-B are the same as equation 43A-B except thatequations 44A-B are for light from LED 7120 incident on LED 7340 asshown in FIG. 73B and equations 45A-B are for light from LED 7230produced by current source 7331 incident on LED 7340 as shown in FIG.73C. Such three equations contain the three independent variables E₂₀,E₃₀, and E₄₀, which are solved for through equations 46-51. Equation 49relates E₄₀ to the known parameters V₄₀₃₀, V₄₀₂₀, and V₃₀₂₀. Thecalculated value for E₄₀ is then applied to equations 45 and 44 to formequations 50 and 51 that determine E₃₀ and E₂₀ respectively.

FIGS. 73A-C provide one of many possible methods to determine theintensity of light produced by a group of LEDs by measuring LEDphotosensitivity. For instance light induced current instead of voltagecan be measured or some combination of current and voltage can bemeasured. When measuring light induced current, an LED can be reversebiased or short circuited for instance. The number of LEDs used todetermine emitted power can be 2 provided both LEDs peak emissionwavelengths are similar or more than 3. The color of the LEDs can be anycombination of colors or one single color. The LEDs can be arranged sideby side with scattered light detected by adjacent LEDs or with lightreflected by a mirror for instance. The product comprising the LEDs cana lamp, a display, or display backlight for instance.

FIGS. 74A-D illustrate a more precise method to determine the intensityof light produced by LEDs 20, 30, and 40 which uses a fixed light source60 as a known reference that eliminates variations in the relationshipbetween LED emitted power and photosensitivity. In this example LEDs 30and 40 have approximately equal peak emission wavelengths and LED 20 hasa shorter peak emission wavelength. The following equations areassociated with FIGS., 74A-D. In particular, equations 52A-B and 53A-Bare associated with FIG. 74A. Equations 54A-B are associated with FIG.74B. Equations 55A-B are associated with FIG. 74C. Equations 58A-B areassociated with FIG. 74D. And equations 56, 57 and 59 utilize the otherequations.

V _(a30) /V _(a30) =V ₃₀=(C ₃₀)(E _(a30) /E _(n30))=C ₃₀ E ₃₀  [EQ. 52A]

E ₃₀ =V ₃₀ /C ₃₀  [EQ. 52B]

V _(a40) /V _(n40) =V ₄₀=(C ₄₀)(E _(a40) /E _(n40))=C ₄₀ E ₄₀  [EQ. 53A]

E ₄₀ =V ₄₀ /C ₄₀  [EQ. 53B]

V _(a30)=(V _(n3040))(C ₃₀)(E ₃₀)(E ₄₀)  [EQ. 54A]

V _(a30) N _(n3040) =V ₃₀₄₀=(C ₃₀)(E ₃₀)(E ₄₀)  [EQ. 54B]

V _(a40)=(V _(n4030))(C ₄₀)(E _(a40))(E ₃₀)  [EQ. 55A]

V _(a40) /V _(n4030) =V ₄₀₃₀=(C ₄₀)(E ₄₀)(E ₃₀)  [EQ. 55B]

Substituting 52B into 54B provides:

V ₃₀₄₀=(C ₃₀)(V ₃₀ /C ₃₀)(E ₄₀)

E ₄₀=(V ₃₀)(V ₃₀₄₀)  [EQ. 56]

Substituting 53B into 55B provides:

V ₄₀₃₀=(C ₄₀)(V ₄₀ /C ₄₀)(E ₃₀)

E ₃₀=(V ₄₀)/(V ₄₀₃₀)  [EQ. 57]

V _(a30)=(V _(n3020))(C ₃₀)(E ₃₀)(E ₂₀)  [EQ. 58A]

V _(a30) /V _(n3020) =V ₃₀₂₀=(C ₃₀)(E ₃₀)(E ₂₀)  [EQ. 58B]

Substituting 52B into 58B provides

V ₃₀₂₀ =V ₃₀)(E ₂₀)

E ₂₀ =V ₃₀₂₀ /V ₃₀  [EQ. 59]

Light source 7460 emits a fixed and known amount of light E₁ on LEDs7230 and 7340, which induces voltages V_(a30) and V_(a40) acrossresistors 7232 and 7342 respectively. Equations 52A-B relate the ratioof actual voltage V_(a30) over the nominal voltage V_(a30) generated bya group of LEDs representative of LED 7230 in response to light source7460 to the ratio of actual optical power E_(a30) emitted by LED 7230when driven with a fixed current over the nominal optical power E_(a30)emitted by a group of LEDs representative of LED 7230 when driven with afixed current as shown in FIG. 74A. Since the light power emitted by anLED is not perfectly correlated with the photosensitivity of such LED,equations 52A-B introduce a correction coefficient C₃₀ that preciselydefines the relationship between such ratios. Equations 53A-B are thesame as equations 52A-B except for LED 7340 instead of LED 7230 as shownin FIG. 74A.

After light source 7460 illuminates LEDs 7230 and 7340 for sufficienttime to measure voltages V_(a30) and V_(a40), light source 7460 isturned off. Subsequently, LED 7340 is turned on using current source7441 and illuminates LED 7230 with actual optical power E_(a40), whichinduces the voltage V_(a30) across resistor 7232 as shown in FIG. 74B.Equations 54A-B relate the ratio V₃₀₄₀ of V_(a30) over the nominalvoltage V_(a3040) generated by a group of LEDs representative of LED7230 in response to a nominal optical power E_(a40) emitted by a groupof LEDs representative of LED 7340 to the ratios E₃₀ and E₄₀ of theactual optical power emitted by LEDs 7230 and 7340 when driven by fixedcurrents over the nominal optical power emitted by groups of LEDsrepresentative of LEDs 7230 and 7340 when driven by the same such fixedcurrent respectively. As in equations 52A-B, the constant C₃₀ determinesthe relationship between V₃₀₄₀ and the product of E₃₀ and E₄₀.

Subsequent to LED 7340 illuminating LED 7230, LED 7230 then illuminatesLED 7340 with actual output power E_(a30), which induces the voltageV_(a40) across resistor 7342 as shown in FIG. 74C. Equations 55A-B arethe same as equations 54A-B except with LED 7230 and 7340 reversed.Substituting equation 52B into equation 54B yields equation 56 with E₄₀expressed as a function of the measured values V₃₀ and V₃₀₄₀. Likewise,substituting equation 53B into equation 55B yields equation 57 with E₃₀expressed as a function of the measured values V₄₀ and V₄₀₃₀.

Subsequent to determining the actual optical power emitted by LEDs 7230and 7340, the actual optical power E_(a20) emitted by LED 7120 can bedetermined by illuminating LED 7230 with light from LED 7120, whichproduces the voltage V_(a30) across resistor 7232 as shown in FIG. 74D.Equations 58A-D are the same as equations 54A-B and 55A-B except withLEDs 7120 illuminating LED 7230 instead of LED 7340 illuminating LED7230 and LED 7230 illuminating LED 7340 respectively. Substitutingequation 52B into equation 58B yields equation 59 with E₂₀ determined bythe ratio of V₃₀₂₀ over V₃₀.

As in FIGS. 73A-C, FIGS. 74A-D represent one of many possible methods todetermine the intensity of light produced by a group of LEDs bymeasuring LED photosensitivity. Light induced current instead of voltagecan be measured or any combination of current and voltage can bemeasured to determine output intensity. The number of LEDs can be two orany number more than 2. The LEDs can be any combination of colors or anysingle color provided that two LEDs in the group have approximately thesame peak emission wavelength that is approximately equal to or longerthan the peak emission wavelength of the light source if monochromatic.Monochromatic or broad spectrum light sources can be used and multiplelight sources with different spectrums can be used. The two LEDs withapproximately equal peak emission wavelengths (the same color) can betwo red LEDs from adjacent pixels in an RGB display or two strings ofred LEDs in a lamp for instance.

FIGS. 75A-C and FIGS. 75D-F in combination with the method illustratedin FIGS. 73A-C represent two possible methods of approximatelydetermining the actual output power emitted by LEDs 7120, 7230, and 7340over lifetime. Subsequent to intensity calibration during themanufacturing of a device comprising LEDs 7120, 7230, and 7340 using themethod described in FIGS. 74A-D for instance, the voltages V_(n3020),V_(n4020), and V_(n4030) are measured and stored in some form ofnon-volatile memory. According to the method illustrated in FIG. 75A-C,current sources 7121 and 7331 produce the nominal current I₀ used duringthe calibration method described in FIGS. 74A-D for instance, andaccording to the method illustrated in FIG. 75A-C, the current sources7121 and 7331 are adjusted to output the nominal optical power. Thecolor point and intensity of light produced by LEDs 7120, 7230, and 7340are adjusted by turning such LEDs in FIG. 75A-C off for differentpercentages of time using commonly known pulse width modulating (PWM)techniques, while the color point and intensity of light produced bysuch LEDs in FIG. 75D-F are adjusted by changing the current produced bycurrent sources 7121, 7331, and 7441.

After operating a device comprising LEDs 7120, 7230, and 7340 for sometime, the actual optical output intensity from each such LED 7120, 7230and 7340 may change and can be re-measured according to the methodillustrated in FIG. 73A-C using the stored open circuit voltagesV_(n3020), V_(n4020), and V_(n4030) as the nominal voltages. Such methoddetermines the change in emitted output intensity from the change involtage, which is approximately proportional. Such measurements ideallyshould be performed when ambient light is small in comparison to theintensity of light produced by LEDs 7120 and 7230 and incident on LEDs7230 and 7340. The intensity of such ambient light can be determined bymeasuring the open circuit voltage across any LED 7120, 7230, or 7340when all LEDs 7120, 7230, and 7340 are turned off. In the presence ofambient light, the effects of such light can be removed by calculatingthe current induced by such ambient light and removing such current'saffect on the measurements of V₃₀₂₀, V₄₀₂₀, and V₄₀₃₀ illustrated inFIGS. 73A-C.

FIGS. 75A-C and 75D-F illustrate two of many possible methods ofdetermining the change in optical power emitted by LEDs over lifetime bymeasuring the photosensitivity of such LEDs. For instance, the currentinduced by incident light can be measured instead of voltage. The numberand configuration of such LEDs can be different from the threeillustrated in FIGS. 75A-C and 75D-F, which represents a possibleoptical power measurement method for a combination of three red, green,and blue LEDs. For instance, two LEDs with approximately the same peakemission wavelength can measure each other's change in emissionintensity. Additionally, a fixed intensity light could illuminate theLEDs and the LED emission intensity could be determined according to themethod illustrated in FIGS. 74A-D for instance.

FIGS. 76A-D illustrate an example method of determining the relativeintensity of light emitted by LEDs 7120, 7230, and 7340 where two suchLEDs 7230 and 7340 have approximately equal peak emission wavelength andLED 7120 has a peak emission wavelength approximately equal to orshorter than that of LEDs 7230 and 7340. As an example, LEDs 7230 and7340 could be red and LED 7120 could be white, green, or blue. Asanother example, in an array of red, green, and blue LED groups orpixels, the red LEDs of two adjacent groups or pixels of a red, green,and blue LED could be used as LEDs 7340 and 7230, and LED 7120 cansequentially be the two green and the two blue LEDs in such two adjacentgroups or pixels used one at a time as LED 7120.

The following equations are associated with FIGS. 76A-D. In particular,equations 60 and 61 are associated with FIG. 76A. Equation 62 isassociated with FIG. 76B. Equation 63 is associated with FIG. 76C.Equation 64 is associated with FIG. 76D. And equations 65, 66 and 67utilize the other equations.

R _(x)=(C _(u))(E _(ax) /E _(mx))  [EQ. 60]

V _(a30) /V _(n3040) =V ₃₀₄₀=(R ₃₀)(E ₄₀)  [EQ. 61]

V _(a40) /V _(n4030) =V ₄₀₃₀=(R ₄₀)(E ₃₀)  [EQ. 62]

V _(a30) /V _(n3020) =V ₃₀₂₀=(R ₃₀)(E ₂₀)  [EQ. 63]

V _(a40) /V _(n4020) =V ₄₀₂₀=(R ₄₀)(E ₂₀)  [EQ. 64]

Ratio of 61 over 63 provides:

V ₃₀₄₀ /V ₃₀₂₀=(R ₃₀)(E ₄₀)/(R ₃₀)(E ₂₀)(E ₄₀)(E ₂₀)  [EQ. 65]

Ratio of 62 over 64 provides

V ₄₀₃₀ /V ₄₀₂₀=(R ₄₀)(E ₃₀)(R ₄₀)(E ₂₀)=(E ₃₀)(E ₂₀)  [EQ. 66]

Ratio of 65 over 66 provides:

(V ₃₀₄₀ /V ₃₀₂₀)/(V ₄₀₃₀ /V ₄₀₂₀)=(E ₄₀)/(E ₂₀)(E ₃₀ /E ₂₀)

(V ₃₀₄₀)(V ₄₀₂₀)/(V ₄₀₃₀)(V ₃₀₂₀)=E ₄₀ E ₃₀  [EQ. 67]

In such method, LED 7340 first illuminates LED 7230 as shown in FIG. 76Ato create equation 61, which relates the ratio V3040 of voltage Va30over the nominal Vn3040 produced when LED 7230 is illuminated with thenominal optical power to the ratio E40 of the actual emitted opticalpower Ea40 over such nominal optical power. The proportionality factorbetween V3040 and E40 is the normalized responsivity of LED 7230 definedas R₃₀ using the general responsivity equation set forth as equation 60.Subsequently, LED 7230 illuminates LED 7340 as shown in FIG. 76B andthen LED 7120 illuminates both LEDs 7230 and 7340 as shown in FIGS. 76Cand 76D to form equations 62, 63 and 64 respectively.

As shown in equation 65, the ratio of equation 61 over 63 provides therelative emitted power between LED 7340 and 7120. Likewise, equations 66and 67 provide the relative power emitted power between LED 7230 and7120, and between LED 7340 and 7230 respectively. Such equations providethe relative optical power emitted by all three LEDs from measurementsof induced voltages so that compensation circuits can adjust the emittedintensity from each LED to produce a precise color or to maintain afixed color over the lifetime of the LEDs.

FIG. 77 is an example block diagram for circuitry that can implement themethods illustrated in FIGS. 73A-C, 74A-D, 75A-C, 75D-F, and 76A-D whichcomprises driver integrated circuit 7780, LEDs 7120, 7230, and 7340, andresistors 7232 and 7342. Integrated circuit 7780 further comprisestiming and control circuitry 7781, coefficient matrix 7782, digital toanalog converter (DAC) 7783, analog to digital converter (ADC) 7784, andthree output drivers 7785 for producing currents for LEDs 7120, 7230 and7340. Output drivers 7785 further comprise of pulse width modulators7787 and current sources 7786.

Timing and control circuitry 7781 manages the functionality of driver IC7780. Illumination data for LEDs 7120, 7230, and 7340 is eitherhardwired into timing and control circuitry 7781 or is communicated totiming and control circuitry 7781 through some means, and is forwardedat the appropriate time to the color correction matrix 7782. Colorcorrection matrix 7782 can, among other things, adjust the illuminationdata for LEDs 7120, 7230, and 7340 to compensate for variations betweenLEDs to produce uniform brightness and color across a display or from alamp. Matrix 7782 can comprise correction coefficients that whencombined with the illumination data produce the data forwarded to outputdrivers 7785, which have pulse width modulators 7787 that produce logiclevel signals that turn current sources 7786 on and off to LEDs 7120,7230, and 7340.

ADC 7784 has access to terminals of all 3, in this example, LEDsconnected to driver IC 7780 and can, among other things, measure thevoltage produced across resistors 7232 and 7342 in response to lightincident on LEDs 7230 and 7340. The anodes of all three LEDs in thisexample can be tied together to a single supply voltage Vd 7788, or canbe connected to different supply voltages. In the case all three LEDs7120, 7230, and 7340 are of one color, all anodes preferentially wouldbe connected together. In the case, such three LEDs 7120, 7230, and 7340are of different colors, each such different color LED 7120, 7230, and7340 would preferentially be connected to each such different supplyvoltage.

FIG. 77 is just one example of many possible driver IC 7780 blockdiagrams. For instance PWM 7787 would not be needed if LEDs 7120, 7230,and 7340 were driven with variable current for fixed amount of times.Resistors 7232 and 7342 would not be needed if ADC 7784 measured opencircuit voltage, short circuit current, or some other combination ofcurrent and voltage from LEDs 7120, 7230, and 7340. DAC 7783 could be afixed current source if variable currents were not desired.

FIG. 78 is an example block diagram of correction matrix 7782 that cancorrect for variations in light intensity produced by a combination ofred, green, and blue LEDs 7120, 7230, and 7340 to produce relativelyuniform brightness and color across a display or from a lamp. Matrix 82comprises memory 7890 that can store correction coefficients Cr, Cg, andCb, which are combined by multipliers 7891 with the red, green, andblue, for instance, illumination data respectively from timing andcontrol circuitry 7781 to produce the illumination data forwarded tomodulators 7787 controlling red, green, and blue LEDs 7120, 7230, and7340 respectively. Such correction coefficients are typically relativelylarge, which produce adjustments in the illumination data to compensatefor variations between LEDs 7120, 7230, and 7340.

Memory 7890 can be made from SRAM, DRAM, FLASH, registers, or any otherform of read-writable semiconductor memory. Such correction coefficientsperiodically can be modified by driver IC 7780 or any other processingelement in a display or lamp for instance to adjust for changes in LEDs7120, 7230, and 7340 characteristics for instance over temperature orlifetime.

Multipliers 7891 scale the illumination data from timing and controlcircuitry 7781 by multiplying each color component by the correspondingcorrection coefficient. Such multiplication can be performed by discreethardware in bit parallel or bit serial form, in an embeddedmicrocontroller, or by any other means. Preferentially, one hardwaremultiplier comprising a shifter and an adder performs all threemultiplications. As such, FIG. 78 is just one of many possible blockdiagrams for correction matrix 7782.

FIGS. 79A-C illustrate one possible method to determine the peakemission wavelength λ_(p) from an LED by determining such LED'sphotosensitivity as a function of the wavelength of light incident onsuch LED. Such measurement system could comprise light source 7460, LED7230 and resistor 7232 as illustrated in FIG. 74A, with the wavelengthof light emitted by light source 7460 switched between wavelengths λ⁻and λ₊ that are slightly shorter and longer respectively than theexpected peak emission wavelength λ_(p) of LED 7230.

Plot 7900 in FIG. 79A represents the photosensitivity of LED 7230 with anominal peak emission wavelength λ_(pn) as a function of incidentwavelength with the vertical axis representing the voltage inducedacross resistor 7232. At wavelengths longer than λ_(pn), thephotosensitivity reduces significantly, while at wavelengths shorterthan λ_(pn), the photosensitivity reduces linearly with wavelength. Alsoshown is incident light with wavelength λ⁻ producing voltage V⁻ acrossresistor 7232 and incident light with wavelength λ₊ producing voltage V₊across resistor 7232. Line 7903 connecting the points (λ⁻, V⁻) and(λ₊,V₊) has a slope M=(V−−V+)/(λ⁻−λ₊).

Plot 7901 in FIG. 79B illustrates the photosensitivity of an LED 7230with a peak emission wavelength λ_(p−) that is slightly shorter than thenominal peak emission wavelength λ_(pn). When such an LED 7230 isilluminated by light source 7460 with wavelengths λ⁻ and λ⁻, voltages V⁻and V₊ respectively are generated across resistor 7232. The differencein voltage between such V⁻ and V₊ is greater for such LED 7230 with peakemission wavelength λ_(p−) that is slightly shorter than the nominalpeak emission wavelength λ_(pn) than for such LED 7230 with the nominalpeak emission wavelength λ_(pn). Additionally, the slope M of line 7904is more negative for the LED 7230 emitting the peak wavelength λ⁻, thanfor the LED 7230 emitting the nominal peak wavelength λ_(pn).

Plot 7902 in FIG. 79C illustrates the photosensitivity of an LED 7230with a peak emission wavelength λ_(p+) that is slightly longer than thenominal peak emission wavelength λ_(pn). When such an LED 7230 isilluminated by light source 7460 with wavelengths λ⁻ and λ⁻, voltages V⁻and V₊ respectively are generated across resistor 32. The difference involtage between such V⁻ and V₊ is smaller for such LED 7230 with peakemission wavelength λ_(p−) that is slightly longer than the nominal peakemission wavelength λ_(pn) than for such LED 7230 with the nominal peakemission wavelength λ_(pn). Additionally, the slope M of line 7905 isless negative for the LED 7230 emitting the peak wavelength λ₊, than forthe LED 7230 emitting the nominal peak wavelength λ_(pn).

Since the slopes of lines 7903, 7904, and 7905 are directly related tothe peak emission wavelength of LED 7230, such slopes can be used todetermine such peak emission wavelengths. FIGS. 79A-C illustrate one ofmany possible methods to determine the peak emission wavelength of lightproduced by an LED by measuring the photosensitivity of such LED. Forinstance, LED light induced current could be measured instead of voltageor some other combination of current and voltage could be measured.Additionally, light with broader spectrums of light could induce suchvoltages or currents instead of the mono-chromatic sources illustratedin FIG. 79.

FIG. 80 is an example block diagram for correction matrix 7782 that cancorrect for variations in both light intensity and wavelength producedby a combination of red, green, and blue LEDs 7340, 7230, and 7120 forinstance to produce uniform brightness and color from an array of LEDs.Matrix 7782 comprises memory 7890 that can store nine correctioncoefficients with three such coefficients for each color componentproduced. Coefficients Crr, Cgg, and Cbb would typically be effectivelythe same as Cr, Cg, and Cb from FIG. 78 to adjust for intensityvariations in LEDs 7120, 7230, and 7340, while the remainingcoefficients (Crg, Crb, Cgr, Cgb, Cbr, Cbg) compensate for wavelengthvariations.

For instance, if the red illumination data from timing and controlcircuitry 7781 was intended for an LED 7340 with a wavelength of 650 nmand the connected LED 7340 wavelength was exactly 650 nm, coefficientsCgr and Cbr would be zero and Crr would be close to one. If suchconnected LED 7340 wavelength was 640 nm and had the same intensity asthe just previous example, Crr would be slightly smaller than in thejust previous example and Cgr and Cbr would be non-zero, which wouldproduce some light from such green and blue LEDs 7230 and 7120respectively. The wavelength of the combination of light from such red,green, and blue LEDs 7340, 7230, and 7120 would be perceived the same asmono-chromatic light from a single red LED 7340 emitting at precisely650 nm.

Memory 7890 and multipliers 7891 can operate and be implemented asdescribed for FIG. 78. Adder 8010 sums the multiplication results fromthe three connected multipliers 7891 to produce the illumination dataforwarded to modulators 7887. Such adders 8010 can be implemented inhardware or software, or be performed bit parallel or bit serial. FIG.80 is just one of many possible intensity and wavelength correctionmatrix 7782 block diagrams.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated.

1. A light source having an adjustable color point, comprising: a broadspectrum light emitter; an LED with a peak emission wavelength within aspectrum of the broad spectrum light emitter; and a controllerconfigured to use the LED to measure a portion of the spectrum of thebroad spectrum light emitter and to use the LED to produce illuminationto adjust a color point of the light source.
 2. The light source asrecited in claim 1, wherein the LED is a first LED, and furthercomprising a second LED, wherein the controller is configured to comparea signal induced on the first LED by light from the broad spectrum lightemitter to a signal induced on the first LED by light from the secondLED.
 3. The light source as recited in claim 2, wherein the broadspectrum light emitter is a white LED.
 4. The light source as recited inclaim 3, wherein the white LED comprises a blue LED.
 5. The light sourceas recited in claim 3, wherein the white LED comprises a material toconvert light from one wavelength to other wavelengths.
 6. The lightsource as recited in claim 5, wherein the material to convert light fromone wavelength to other wavelengths is in physical contact with a blueLED.
 7. The light source as recited in claim 3, wherein a peak emissionwavelength of the second LED is within the spectrum of the white LED. 8.The light source as recited in claim 7, wherein the peak emissionwavelength of the second LED is shorter than the peak emissionwavelength of the first LED.
 9. The light source as recited in claim 8,wherein the controller is further configured to combine a signalproduced by the first LED in response to light from the white LED and asignal produced by the first LED in response to light from the secondLED to produce a ratio, and wherein the controller is also configured tocompare the ratio to a desired ratio.
 10. The light source as recited inclaim 9, wherein the controller is configured to adjust a relative lightintensity produced by the broad spectrum light emitter and by the firstLED so that the ratio and the desired ratio are substantially equal. 11.The light source as recited in claim 10, wherein the first LED is greenand the second LED is blue.
 12. The light source as recited in claim 3,further comprising a third LED with a peak emission wavelength longerthan the first LED peak emission wavelength.
 13. The light source asrecited in claim 12, wherein the controller is further configured tocombine a signal produced by the third LED in response to light from thewhite LED and a signal produced by the third LED in response to lightfrom the first LED or second LED to produce a ratio, and wherein thecontroller circuitry is further configured to compare the second ratioto a desired ratio.
 14. The light source as recited in claim 13, whereinthe controller is further configured to adjust a relative lightintensity produced by the light source and the first LED or third LED orboth the first LED and third LED such that the ratio and the desiredratio are substantially equal.
 15. A method for adjusting a color pointfor a light source, comprising emitting a spectrum of light with a broadspectrum light emitter; measuring a portion of the spectrum of the broadspectrum light emitter using an LED having a peak emission wavelengthwithin the spectrum of the broad spectrum light emitter; and using theLED to produce illumination to adjust a color point of the light source.16. The method as recited in claim 15, further comprising comparing asignal induced on the first LED by light from the broad spectrum lightemitter to a signal induced on the first LED by light from a second LED.17. The method as recited in claim 16, wherein the broad spectrum lightemitter is a white LED.
 18. The method as recited in claim 17, whereinthe white LED comprises a blue LED.
 19. The method as recited in claim17, wherein the white LED comprises a material to convert light from onewavelength to other wavelengths.
 20. The method as recited in claim 19,wherein the material to convert light from one wavelength to otherwavelengths is in physical contact with the blue LED.
 21. The method asrecited in claim 17, further comprising using a second LED having a peakemission wavelength within the spectrum of the white LED.
 22. The methodas recited in claim 21, wherein the peak emission wavelength of thesecond LED is shorter than the peak emission wavelength of the firstLED.
 23. The method as recited in claim 22, further comprising combininga signal produced by the first LED in response to light from the whiteLED and a signal produced by the first LED in response to light from thesecond LED to produce a ratio, and comparing the ratio to a desiredratio.
 24. The method as recited in claim 23, further comprisingadjusting a relative light intensity produced by the light source and bythe first LED so that the ratio and the desired ratio are substantiallyequal.
 25. The method as recited in claim 24, wherein the first LED isgreen and the second LED is blue.
 26. The method as recited in claim 17,further comprising providing a third LED with a peak emission wavelengthlonger than the first LED peak emission wavelength.
 27. The method asrecited in claim 26, further comprising combining a signal produced bythe third LED in response to light from the white LED and a signalproduced by the third LED in response to light from the first LED orsecond LED to produce a ratio, and comparing the second ratio to adesired ratio.
 28. The method as recited in claim 27, further comprisingadjusting a relative light intensity produced by the light source andthe first LED or by the lights source and the third LED or the lightssource and the first and third LEDs such that the ratio and the desiredratio are substantially equal.
 29. A controller for a light sourcehaving an adjustable color point, comprising: control circuitryconfigured to be coupled to a broad spectrum light emitter and an LEDwith a peak emission wavelength within a spectrum of the broad spectrumlight emitter, the control circuitry being configured to use the LED tomeasure a portion of the spectrum of the broad spectrum light emitter;and output driver circuitry configured to be coupled to the broadspectrum light emitter and the LED and to use the adjustment LED toadjust a color point for light from the broad spectrum light emitter andthe adjustment LED.
 30. The controller as recited in claim 29, whereinthe LED is a first LED, and wherein the control circuitry is furtherconfigured to be coupled to a second LED, and wherein the controlcircuitry is configured to compare a signal induced on the first LED bylight from the broad spectrum light emitter to a signal induced on thefirst LED by light from the second LED.
 31. The controller as recited inclaim 30, wherein the control circuitry is further configured to combinea signal produced by the first LED in response to light from the broadspectrum light emitter and a signal produced by the first LED inresponse to light from the second LED to produce a ratio, and whereinthe control circuitry is also configured to compare the ratio to adesired ratio.
 34. The controller as recited in claim 33, wherein thecontrol circuitry is configured to adjust a relative light intensityproduced by broad spectrum light emitter and by the first LED so thatthe ratio and the desired ratio are substantially equal.